The art of changing boundaries

In my last post (http://newstonoone.blogspot.com/2015/06/the-boundaries-of-reason-possible-shape.html) I spent some time looking at the likely impact of the impending boundary changes on the numbers of seats in different regions and the potential impact on the seat numbers of different parties.  In this post I shall look at how the detail of the boundary review might assist or hinder the different parties.

National party strategic considerations

What, however, would be better for the national parties?  To answer this, we need to think about what the parties need.  They will simultaneously wish to:

1) Maximise their current notional seat count
2) Maximise their chances of taking new seats
3) Minimise their chances of losing seats
4) Keep incumbents happy

But these aims are inconsistent, so the parties will need to choose which are most important to them.  This will vary for each party.

Right now the Conservatives are fairly content with how things stand.  They have an overall majority on a lead of 6.5% of the national vote share.  They will retain power, however, only if they have a substantial seat lead over Labour so they need to ensure first of all that the smallest possible poll lead will produce the most seats possible.  If they go below that level they're expecting defeat anyway so the margin of defeat is less important than maximising the chances of success at or above that level.

Labour, by contrast, are already in a losing position.  The current shares of votes are unacceptable to Labour and they need to plan on the basis that they are going to do better.  They will want to ensure that small improvements in their vote share will result in as many extra seats as possible.  

From Labour's perspective a reduction in their notional seat count now following a boundary review may not necessarily be bad news if the result is to bring the possibility of winning more seats in play in 2020 should their vote share improve.  They shouldn't be planning on the basis of their current vote share: that is a losing proposition, as we saw in May.  

For example, York Central and York Outer are respectively a safe Labour and safe Conservative seat.  If they were combined and then divided on a homogeneous basis, the Conservatives would have two marginal seats that would both fall on a swing of just over 3% to Labour.  Labour might conclude that such a reorganisation might suit them if they were working on the basis that a swing of 3% was the minimum that they were targeting.

So each party needs to identify a seat share that they regard as the minimum acceptable and then take decisions on the boundary review with that in mind.  There is no point in Labour giving up a seat in the manner described above if it is not going to be recouped on a smaller swing than that presently required for their target number of gains.  And there is no point in the Conservatives seeking a redistricting that results in a notional gain on current vote shares if it makes retaining power on a slightly lower vote share harder.

Selling the strategy to incumbents may on occasion prove difficult and that cannot be overlooked.  In particular, the Conservatives want to get the boundary changes through if they can since it will in general benefit them.  So they don't want to upset incumbents unduly: they have a vote on the matter.  It may be better to get an arrangement that isn't the very best for the national party if it is decent enough and keeps an incumbent happy.

As for the best tactic for each party in a given area, much will depend on the detail of local voting patterns.  

Developing strategy into tactics

But some general tactics are apparent.

For now, let's work on the basis that the reduction in seats to 600 takes place.  Based on the national total of registered voters in the May 2015 of 46,425,476, that would produce a range of possible seat sizes of 73,508 to 81,244 registered voters with a par of 77,376 voters.

In the south of England, Labour's weakness actually simplifies its strategy.  Some seats will look likely to drift out further of Labour's reach as a result of the reduction in seat numbers and these strict limits on seat sizes - larger seats will generally favour the party that is dominant in the area still further.  

The process will be uneven.  For example, on the general election registered voter numbers Cambridgeshire and Suffolk would be due an additional seat between them even with a seat reduction from 650 to 600.  Meanwhile, Peterborough is below the minimum number of registered voters so it will need to take on more rural (and presumably Conservative-voting) voters from an adjoining constituency.  Ipswich, another constituency where Labour has a keen interest, is likely to suffer the same fate, being a constituency only just above the minimum threshold for registered voters in a county which elsewhere has oversized constituencies.

But some seats where Labour are interested will actually need to be reduced in size.  In more populous seats in which Labour have some strength, like Watford and Waveney, Labour will be looking to shed outlying rural districts from the constituency which will be presumed to be more Conservative in the hope of creating a Labour seat.

In less populous adjacent constituencies with Labour strength, Labour will seek to construct a new seat which takes the best of their support from both.  The tactics here can be trickier.  Both Luton seats are undersized.  Do Labour seek to have the core made into a single seat, accepting the loss of a single seat but creating a single Labour stronghold, or do they accept the attachment of large rural areas to each in the hope of getting both but risking losing both?  Given their current seat tally, they need to take the chance, I think.  This gives the concept of political betting a whole new meaning.

Minor problems

So far I have had much to say about Labour/Conservative battles in the south.  But the smaller parties need to watch out.  For example, the Conservatives will be keen to disrupt UKIP so far as possible.  It would be utterly unsurprising if the Conservatives proposed an arrangement in Essex which left the current Clacton constituency bisected, halving the effect of Douglas Carswell's formidable incumbency and swamping both new constituencies with Conservative voters.  This constituency is going to need some adjustment, being underweight in registered voters, and the Conservatives will want to make it as difficult as possible for him.  

I expect that Labour will have similar thoughts about Brighton and may well seek to despatch Caroline Lucas by providing her with a new cohort of Labour voters to challenge her grip on her seat or partitioning the seat out of existence.  And both main parties may well seek to partition isolated Lib Dem constituencies like Southport, Sheffield Hallam, North Norfolk and Leeds North West.  Even as the electorate becomes less and less inclined to vote for one of the two main parties, the minor parties will find it harder to get or keep Parliamentary representation.

Major problems

By means such as those I described above, Labour managed in the mid-1990s to get a boundary review that actually worked against the Conservatives by bringing into play seats that would not previously have fallen on a landslide.  Might such tactics work again?  It would be much harder this time, as can be illustrated with four pictures:

  

In these four areas, Labour have over 100 seats in solid blocks.  All four blocks will suffer substantial reductions in seats under the review. If the seat count is reduced to 600, three of the 18 Labour seats in Birmingham and the Black Country, one of the four Labour north east Welsh seats, two of the 18 English Labour seats in and around Merseyside, two of the 22 Labour seats in and around Manchester, three of the 26 Labour seats in the north east and four of the 19 Labour South Wales seats look set to go.  That's nearly a third of the seat count reduction accounted for already (and the seven seat reduction in Scotland and two seat reduction in Northern Ireland will do the Conservatives no harm either, taking us up to 24 seats lost from Parliament without the Conservatives having to leave the sofa). 

The chances of offloading any of these 15 seat losses in Labour heartlands onto other parties looks limited, given the solid nature of these Labour blocks, painstakingly built over a generation.  Labour will be doing well if it avoids a dozen notional seat losses in its heartlands before it gets started. 

Conclusions

A reduction in seat count to 600, if achieved, is likely to benefit the Conservatives nationally considerably.  It would be bad for Labour and particularly bad for the Lib Dems, with serious challenges for both the Greens and UKIP.  Each party would need to think carefully about how best to protect its position, bearing in mind what they are trying to achieve in 2020 rather than focussing on what the reorganisation would mean in the context of the May 2015 result.
  But will it be achieved?  Conservative incumbents are going to need a lot of reassurance before they are going to feel able to support it because their seats are likely to be chopped and changed a lot.  That process of reassurance hasn't started yet.  The Conservatives need to decide whether they want to try to get this through.  If they do, they need to start laying the ground right away.



Note

This post first appeared on politicalbetting earlier this afternoon:

http://www2.politicalbetting.com/index.php/archives/2015/06/29/guest-slot-the-art-of-changing-boundaries/

The boundaries of reason: the possible shape of the 2020 election

I previously looked back at the impact of demographic changes on party politics from 1992 to 2015.  That's all well and good, but what changes can we expect for 2020?  To determine that we first need to consider what the new boundaries are likely to look like.

 

It might be thought that the future musings of the Boundary Commissions are imponderable, but we have quite a lot of clues to go on.  We should use them.

The terms of any boundary review are closely delimited in legislation.  The following will occur unless the law is changed or the proposed boundary changes are defeated in Parliament:

1) The election will be fought on 600 seats.
2) There will be two Isle of Wight constituencies, a constituency for Orkney & Shetlands and a constituency for Na h-Eileanan an Iar.
3) The 600 seats will be allocated between England, Wales, Scotland and Northern Ireland according to a strict formula based on the number of registered voters as at the review date in each.
4) Except for the exceptions already noted, the seats will have a population of 95% to 105% of the average constituency size (there are size requirements that are relevant only in Scotland and Northern Ireland has special rules).

These are pretty prescriptive rules. There are already rumblings among Conservative MPs that the seat count should be kept at 650.  As we shall see, this may be in the interests of individual Conservative MPs but it is unlikely to be in the interests of the Conservative party as a whole.

The next thing to realise is that the Boundary Commissions have already started looking at this once (until their work was brought to a juddering halt by the Lib Dems ganging up on their coalition partners: as we shall see, this was absolutely correct from a narrow party interest).  So we already can see the general direction of travel.

For the moment I'm going to work on the basis of a 650 seat Parliament to explore what difference the boundary review might make.  While this is not what the law currently requires, it makes it easier to see what difference the impact of movements in registered voters might have.

Allocation of seats around the component parts of the UK

So, what should we expect?  The first thing to do is to determine the number of registered voters in each part of the UK.  This will be set at the end of this year, so we don't have the precise figures, but the numbers from the general election should provide a fairly decent guide.  We have the electoral commission's preliminary results:

http://www.electoralcommission.org.uk/__data/assets/excel_doc/0011/189623/2015-UK-General-election-data-collated-results-WEB.xlsx                                                                                                          

This gives a national total of registered voters of 46,425,476.

I've separated these out into the component parts of the UK:

https://www.dropbox.com/s/1k6q9vae8sn61xl/Registered%20voters%20and%20turnout.xlsx?dl=0

From these we can derive the following totals of registered voters:

Northern Ireland:1,236,683
Wales: 2,282,297
Scotland: 4,094,784
England: 38,811,712

When the seat allocation is eventually determined, it is done by a broadly proportionate approach.  Since we don't have the relevant registered voter numbers yet, it is pointless doing anything more than a pro rata approach.  If the seat allocation stays at 650, we can expect Northern Ireland to get roughly 17 seats, Wales to get roughly 32 seats, Scotland to get roughly 57 seats and England to get roughly 543 seats (with one seat up for grabs).  If the seat reduction to 600 seats takes effect, we can expect Northern Ireland to get roughly 16 seats, Wales to get roughly 30 seats, Scotland to get 52 or 53 seats and England to get 501 or 502 seats.  This is almost exactly what the allocation would have been if the boundary review had gone ahead last time.  So much for all the fuss about the voter registration changes.

 

Either way, English MPs will become still more dominant in Parliament.  This can only be good news for the Conservatives, who dominate much of England and rely on it for almost all of their seats.

Allocation of seats within England

Just as important as how the seats are distributed in the UK is how the seats will be distributed in England.  The Boundary Commission for England is not legally obliged to follow the same approach when allocating seats between English regions, but in practice it intended to do so in the last Parliament and I expect it to do so again this time.

http://webarchive.nationalarchives.gov.uk/20131002112547/http://consultation.boundarycommissionforengland.independent.gov.uk/wp-content/uploads/2011/08/406678_Guide-to-the-2013-Review_acc.pdf

The English regions had registered voter totals at the general election as follows:

Eastern: 4,364,656
East Midlands: 3,350,769
London: 5,401,616
North East: 1,941,841
North West: 5,240,724
South East: 6,419,548
South West:4,076,494
West Midlands: 4,140,587
Yorkshire & the Humber: 3,875,477

This would result in the following seat allocations, based on England having 543 seats in a 650 seat Parliament (I have assumed a 650 seat Parliament for ease of comparability):

Region	Share of registered voters	New seat count	Old seat count	Change in seat count
Eastern	11.2%	61	58	3
East Midlands	8.6%	47	46	1
London	13.9%	76	73	3
North East	5.0%	27	29	(2)
North West	13.5%	73	75	(2)
South East	16.5%	88*	84	6
South West	10.5%	57	55	2
West Midlands	10.7%	58	59	(1)
Yorkshire and the Humber	10%	54	54	-

 *Plus two Isle of Wight constituencies

Again, this seems to benefit the Tories.  More seats are being added in their strongest areas while the seat count in the North West and the North East, two of their weaker areas, continues to decline.

Putting numbers on these changes

So, what would these movements mean in real seat numbers?  Unfortunately, we cannot simply apply a formula because much depends on how the boundaries are actually set.  Thinking about the detail of boundary commission reviews will need to be the subject for another post, but some general principles can be laid down now.

1) Boundary reviews are bad for incumbents.  The more extensive the boundary alterations, the less of an advantage incumbency gives.

2) Within an area, a seat reduction will increase the advantage of the party with the most support.  To give an extreme example, if Wales were reduced to one constituency, Labour would expect to take 100% of seats in the area.  Considered on a wider scale, it would obviously be to Labour's detriment to have only one seat within Wales, but within Wales itself it would accentuate its political dominance.

3) With a seat reduction in an area, regional strength of trailing parties will outweigh general strength in the area.  For example, if Wales were reduced to four constituencies, Labour might reasonably hope to take all four constituencies.  But it would probably be most worried about losing a seat to Plaid Cymru because of its regional strength in north west Wales.  The fact that the Conservatives poll twice Plaid Cymru's vote share across Wales as a whole would not affect this calculation.

4) An increase of seats in an area will naturally tend to produce more seats for the dominant party in the area, but the increased granularity may help another party gain an odd seat where a pocket of support has previously been swamped by the dominant party's support in previously-attached areas (this is the inverse of the last two points).  For example, Peterborough is a Conservative-held marginal seat comprising a city with outlying areas attached.  Making the reasonable assumption that the city is more Labour-leaning than the outlying areas, I infer that if the seat count in the area were increased and the boundaries were confined more tightly around the town, Labour might hope to pick up a new seat in an area of Conservative dominance.  Incidentally, this will tend to work better for Labour than for the Conservatives, given the way in which Labour support tends to cluster in towns.

With these principles in mind, and without going through the detail of my thought process (which is more art than science in any case), my guess is that if the votes cast in May were cast on the boundaries of a new 650 seat Parliament that I have outlined above, the seat count would be something like:

Conservative: 335
Labour: 229
SNP: 55
Lib Dem: 8
Plaid Cymru: 3
UKIP: 1
Green: 1
Speaker: 1
Northern Irish parties: 17

So I imagine a hypothetical increase in the Conservative majority by ten or so, but it wouldn't fundamentally alter the dynamics of the next election.  I feel that I have made midpoint assumptions in coming to these numbers.

The impact of switching to a 600 seat Parliament

But as the law stands, the boundary review will be conducted on the basis that we will get a 600 seat Parliament, and that will intensify some of the effects that I have just noted.  The new 600 seat Parliament would be comprised roughly as follows:

Scotland: 52
Wales: 30
Northern Ireland: 16
England: 502
     - Eastern 56
     - East Midlands 43
     - London 70
     - North East 25
     - North West 68
     - South East 83 (including two Isle of Wight constituencies)
     - South West 53
     - West Midlands 54
     - Yorkshire & The Humber 50

The seat reorganisation would be relatively minor in the Eastern, South East and South West regions, given the minor adjustments in seat counts, and these are as it happens all overwhelmingly Conservative areas.  They would, however, be very extensive in Wales, the North West and the North East: all Labour areas (Scotland also would be seriously affected).  Of the Conservative-leaning areas, only the West Midlands would see heavy reorganisation.

The consequence might well be that the bulk of Conservative incumbents could see their incumbency damaged in only minor ways, while Labour incumbents would be much more likely to see their incumbency seriously affected.

It gets worse for Labour.  Many of the constituencies with the lowest number of registered voters are in contiguous Labour-held areas.  On a shrinking seat count determined by numbers of registered voters, that is the worst permutation for a party, because there is much less scope to recoup lost seats in the area by taking seats of a rival party.  Leeds, Bradford, Hull and Liverpool are all stuffed full of constituencies with very low numbers of registered voters, all with large Labour majorities.  If the seat count in those areas is reduced, that will probably come straight off the top of the Labour seat total.

Meanwhile, the smaller parties all get hit still harder because of the consequences of reducing the seat count noted above.

My artist's impression of how the results of the last election might have translated onto reasonably normal boundaries on the new basis is something like the following:

Conservatives: 316
Labour: 209
SNP: 50
Lib Dems: 5
Plaid Cymru: 2
UKIP: 1 (maybe)
Greens: 0
Speaker: 1
Northern Ireland: 16 

By this stage, the Conservative majority, now hypothetically 32, is starting to look very solid given the smaller size of the House.  Again, I don't feel that I have particularly stepped out in one direction or another.

So if you want to see why the Opposition (and the Lib Dems in particular) might seek to block the boundary review, this is why.  Their task is hard enough, without the Conservatives being given a still greater head start.



Note

This post first appeared on politicalbetting yesterday:

http://www2.politicalbetting.com/index.php/archives/2015/06/25/guest-slot-the-boundaries-of-reason/

The long view: comparing the 1992 and the 2015 election results

We spend much time looking at the most recent developments.  But every now and then it is profitable to stand back and look at longer term trends.  That is most easily done by comparing elections which produced quite similar overall results and then looking at the detail.  The 1992 and the 2015 election results are sufficiently similar overall to make that a valuable exercise.  Except in Scotland.  

The overall result in 2015 was as follows:

 

Con 330 

Lab 232 

SNP 56 

Lib Dem 8 

Plaid Cymru 3 

UKIP 1 

Green 1 

Speaker 1

Northern Irish parties 18

http://researchbriefings.parliament.uk/ResearchBriefing/Summary/CBP-7186#fullreport
 

The result in 1992 was as follows:

Con 336

Lab 271

Lib Dem 20

Plaid Cymru 4

SNP 3

Northern Irish parties 17

(The outgoing Speaker had retired).

http://www.parliament.uk/documents/commons-information-office/m13.pdf

 

As you can see, the Conservatives tallied much the same seat count in both elections, Labour did considerably better in 1992, as did the Lib Dems, while the SNP went from nowhere to third place.  For Lib Dems surveying these two election results, it must feel like clogs to clogs in five elections.  They have fewer seats now than they had then. The only seat held in both elections is Orkney & Shetland.

Let's start with the big point of difference, Scotland.  In 1992, the SNP were nowhere.  They had fewer seats than Plaid Cymru.  It is easy to forget, but the Conservatives as well as Labour and the Lib Dems had substantial seat numbers in Scotland.  A generation on and the landscape is unrecognisable. 

Scotland's seat count has declined by 13, reducing its numerical significance in Parliament even as demands for independence and further devolution have catapulted up the political agenda.  And the SNP have effectively wiped the other three parties off the map.  In the same period, Plaid Cymru have gone nowhere.

This is, of course, a disaster for Labour who at a stroke have lost a large block of MPs.  They will either need to be recovered or replaced elsewhere.  Right now, the latter looks much more achievable.

 

If we look at just England and Wales, the results converge:

 

1992

Con 325

Lab 222 

Lib Dem 11 

Plaid Cymru 4 

2015

Con 329 

Lab 231 

Lib Dem 7 

Plaid Cymru 3 

UKIP 1 

Green 1 

Speaker 1

 

These results are as close as you will ever get any two election results.  So substantial differences in the detail will have real meaning. 

There were 11 more seats in England and Wales in 2015 than in 1992. But the distribution of the seats has been uneven. Despite the rapid population growth of London, there are 11 fewer seats in greater London now than in 1992 (the newcomers must in large part be non-voting immigrants). There are five fewer seats in the north west and the north east combined than in 1992 (regional boundaries were a little different then).  Meanwhile, there are seven extra seats in the south west, four extra seats in the east midlands, an extra seat in the west midlands, two extra seats in Wales and 13 extra seats in the south east and east. The seats have been accumulating in more Tory-friendly areas over the last 24 years. 

 

And this is the real story. Labour are not taking fewer seats now than in 1992 in the south. They took ten seats in the south west, the south east outside London and the east in 1992 and 12 seats in the same areas in 2015. But the Conservatives, benefiting from this southwards drift of population, are taking 20 more seats in these areas. Labour's failure to find a message for southern England is becoming ever more damaging to their chances. 

 

We see the same picture in the east midlands, where Labour have the same seat tally as in 1992 but the Conservatives have gained ground, pocketing all the increase in seat count in the area. Only the west midlands have decisively swung away from Labour.  

In Wales, Labour have lost a quarter of its vote share in under 25 years (and 40% of its vote share since 1966).  So far it has not significantly affected its seat count, though it is drifting down, because the rest of the vote is still more fragmented with the rise of UKIP.  But Labour looks vulnerable in Wales in the longterm if this trend continues.  The example of Scotland should be fresh in their minds.

If Labour have underperformed in these areas relative to 1992, there are areas of outperformance too. They have increased their stranglehold on the north east and the north west, getting four more seats in these regions even with a reduced seat count to aim at. Most strikingly, they have conquered London, holding 60% of the seats now as opposed to the 40% of seats that they held in 1992.  But again, there are fewer seats in London than there once was.

It is anachronism to refer to the Core Cities in 1992, since this grouping of the largest cities outside London was only set up in 1995.  Labour always found strength in the larger English cities, but Labour have strengthened their position in the English areas now covered by that grouping still further.  In 1992, the seats in what is now covered by the Core Cities in England divided as follows:

Labour: 82
Con: 31
Lib Dem: 2

Now, the split is:

Labour: 83
Con: 16
Lib Dem: 3

The seat count in the Core Cities in England has declined, but Labour are getting ever closer to a whitewash.  55% of all Labour seats are now found in an English Core City or in London.  The perspective of the average Labour MP may be unhealthily influenced by concerns of constituencies that are not particularly representative.

Wherever they have strengthened over the last 23 years, Labour are getting a larger slice of a smaller cake.  Meanwhile, the Conservative-dominated areas of England have gained seats, benefiting the Conservatives by default.  Labour risk being on the wrong side of longterm demographic trends.  

There is another way of looking at this.  Twice at low ebbs Labour have been reduced to nominal seat counts in the rural south, but in better times in the interim they have picked up a lot more seats in those areas.  They simply need to rediscover that art.

Even in good times, however, the Conservatives have found themselves progressively squeezed further out of their weaker areas and are losing London.  Labour have an immediate demographic problem but the Conservatives have a much more enduring demographic problem.  Their room for further progress is limited unless they can unlock more seats in areas that have been turning their backs on them for a generation.  Meanwhile, the distance that they could fall is much greater.  George Osborne is developing policies such as the Northern Powerhouse to appeal to the Core Cities.  Will they be enough?  We shall see, but I doubt it.  Both main parties are facing longterm trends that should trouble them deeply.

2020: Plaid Cymru, waiting for the great leap forward

Plaid Cymru had an election to forget on 7 May 2015.  They marginally improved their vote share across Wales, but found themselves overtaken by UKIP on that measure, with the Lib Dem collapse largely bypassing them.  Their seat tally was unchanged, missing out on Ynys Mon by a whisker and failing by a larger margin to wrest Ceredigion out of Lib Dem hands.  Indeed, in their top ten targets, they lost vote share in all bar three constituencies: Ynys Mon, Rhondda and Cardiff West. 

 

Considering that Plaid Cymru had more election coverage than ever before and featured in the national televised debates, this failure to make any significant advance must be seen as a serious disappointment.  The contrast with the triumph of their fellow nationalists in Scotland in the same election could not be starker.

Plaid Cymru's prospects

What are Plaid Cymru's prospects for 2020? Well, first of all it must be noted that there are likely to be boundary changes, so these lists should not be taken as precise seat targets but as a general indication of where Plaid Cymru may prosper or flounder.  This is particularly important in Wales where any boundary changes are likely to be particularly far-reaching, given the current over-representation in Parliament that Wales enjoys.  A reduction in seat counts is usually more harmful for smaller parties but in the case of Plaid Cymru that may not in fact be the case because its vote is concentrated geographically, being particularly strong in north west Wales.  (It would, however, make UKIP's chances of taking a seat in Wales harder - their support is very evenly spread, not exceeding 20% in any existing constituency.)

Here are the Welsh constituencies organised by diminishing Plaid Cymru vote share:

https://docs.google.com/spreadsheets/d/14JKN65Dy5C3N1vqEEkX_0BSk73v0xExcIFRRiapByzo/edit?usp=sharing

This table was prepared by AndyJS.

Alternatively, here are the Welsh constituencies organised by the swings that Plaid Cymru would require to take each seat:

https://drive.google.com/file/d/0Bygi8eZw-4q1by0wMmNnUVVCZFU/view?usp=sharing

As you can see, Plaid Cymru's prospects differ considerably between the two lists given above.  Which is more useful? 

To determine the answer, we first need to look at a different election in a different part of the UK.

The Scottish great leap forward

In 2010, the SNP made only modest progress in vote share and won no new Westminster seats.  This was their target list in the run-up to this year's election, arranged by swing:

https://docs.google.com/document/d/1WBE7ZiFBcNn8pKRZwwImmfi6eqm3jMKI3Jo_k2m-nEQ/edit?usp=sharing

The SNP required some pretty heroic swings, and by and large it got them.  There does not seem to have been a particularly strong relationship between the seats which it did not win and the swings required to take them.  Edinburgh South and Dumfriesshire, Clydesdale & Tweeddale would require relatively small swings to the SNP while Orkney & Shetland would have required the second largest swing.

However, there is a strong correlation between SNP performance in 2015 and its absolute vote share in 2010, at least at the bottom end of that table.  The ten lowest SNP vote shares in 2010 were (from the bottom up):

Edinburgh South
East Renfrewshire
Berwickshire, Roxburgh & Selkirk
Edinburgh North & Leith
East Dunbartonshire
Dunfermline & West Fife
Orkney & Shetland
Dumfriesshire, Clydesdale & Tweeddale
Aberdeen South
Glasgow North

This list includes all three of the seats that the SNP did not take in 2015 and four of the five most marginal SNP seats for 2020.  It seems that if the mould is broken by a party that soars in the polls, prior vote share is a more reliable guide than swing required as to where the mould will break least.

Revenons a nos moutons

That is all well and good, but Plaid Cymru in 2015 are far behind where the SNP were in 2010.   Their vote share in 2015 across Wales is only just over half what the SNP had across Scotland in 2010.  The SNP was second in vote share in Scotland in 2010 while Plaid Cymru remains fourth in vote share in Wales in 2015.  The SNP was in power in Holyrood and was able to engineer a lengthy and all-consuming debate about national identity between 2010 and 2015.  Plaid Cymru is in opposition in the Welsh Assembly and there is no particular reason to expect that to change next year.  Mould-breaking (and Mold-taking) looks like a distant prospect.

I would pretty much completely discount the chances of Plaid Cymru in any seat where they had not already got at least 15%, even allowing for the fact that the four or five party nature of Welsh politics means that seats can be taken on relatively low vote shares.  On current boundaries, that means that they have a vague interest in just nine seats.  A uniform 5% swing to Plaid Cymru would deliver them just two extra seats on these boundaries.  A uniform 10% swing to Plaid Cymru would deliver them just one more.

But if Plaid Cymru are to make any progress at all, they need to start gaining vote share.  They can't profit by being bystanders while other parties rise and fall.  They need to look at what the SNP has achieved in Scotland, consider how that may be applied to their circumstances in Wales and act accordingly.  Otherwise, they could be waiting for the great leap forward for a very long time indeed.

2020 and the Greens: renewing the energy

What to make of the Greens' performance on 7 May? Despite far more publicity than in previous election campaigns, they took no new seats. They strengthened their hold on Brighton Pavilion and came a clear second in Bristol West, but went backwards in Norwich South.  On the surface, they did not do much better than standing still - a disappointing result for a party that had attracted so much coverage in the election campaign.

Look a little deeper and the Greens have made some progress. Thanks to AndyJS, whose masterly work in processing election data is criminally overlooked all too often, we can look more closely at this progress.

Here are the Greens' results from 2010, ranked in order of vote share:

https://docs.google.com/spreadsheets/d/1Y6K9EfRuZ4AVVHPyXu2rgfhOwd7I-f1xWmj7-YMxrRA/edit#gid=0

And here are the Greens' results from 2015, again ranked in order of vote share:

https://drive.google.com/file/d/0Bygi8eZw-4q1LTA5VThnXzF1MWs/view?usp=sharing

(Both of these tables are AndyJS's.)

In 2010 they contested 335 seats and won an average of 1.81% of the vote in those seats.  In 2015 they contested 573 seats and won 3.77% of the vote (even including the constituencies they did not stand in).  They saved their deposits in 131 seats, up from seven seats in 2010.  The Greens exceeded 10% in only two seats in 2010, but 18 in 2015.  They now have an estimated membership of 66,500.  This is a very substantial number and gives the Greens the ability to undertake a proper ground game.  This is all positive for them.

But let's not get carried away.  UKIP also took only one seat.  But they got more than 10% in 451 seats.  As yet the Greens have nothing like the breadth of support that even UKIP have.

Green strengths

Where are the Greens taking votes?  They are largely an English phenomenon.  They buddied up before the election with the SNP and Plaid Cymru, and the price of doing so seems to have been to ruin their chances in Scotland and Wales.  They saved their deposits in just three seats in each of Scotland and Wales.

If you look at the seats that the Greens did best in, three trends stand out. First, the Greens did well in London.  Ten of their 30 best vote shares are in the capital.  All ten of these are rock solid Labour seats in inner city London.

Next, the Greens have built up significant regional strength in the south west.  Seven of their top 30 vote shares are found in this region.  You should also note that the Greens did not contest Devon East, where a Green-friendly independent scored an impressive 24% of the vote.  With the Lib Dems having lost much of the progressive vote and Labour organisationally weak in this region, the Greens have opportunities to advance further here.

The third trend, which overlaps with the other two, is for the Greens to have done well in areas with high student populations.  This report lists at the end the English constituencies with high student populations (using the 2011 census):

http://www.hepi.ac.uk/wp-content/uploads/2014/12/VERY-FINAL-CLEAN-PDF.pdf

It does so in a not particularly helpful way, so I have reorganised this into a more useful table:

https://drive.google.com/file/d/0Bygi8eZw-4q1ajZQTlFLQ25reEE/view?usp=sharing

Ten of the Greens' top 30 seats by vote share had a student population of 20% or more.  Many of the others also had a substantial student population.  The Greens lost their deposit in only three of the constituencies with a student population of 20% or more: Coventry South, Birmingham Ladywood and Loughborough.

One drawback about being popular with students is that they don't usually hang around the same constituency for two elections running.  But if the Greens can embed themselves more firmly in student politics, the meme of students voting Green could transmit itself from student generation to generation.

So the Greens have three possible strands to pursue in the coming years: inner city London, the south west and student-heavy constituencies.

Green targets

Given the Greens' low vote shares, it does not make sense to prepare a list of targets created exclusively by swing required - as we have already seen with the Lib Dems and UKIP, such lists will be dominated by constituencies where the winner had a low share of the vote, regardless of whether there is any base level of support for the minority party.  Having seen that effect with both the Lib Dems and UKIP, I have decided to create a 30 seat target list based on the 30 seats where the Greens had the highest share of the vote.  (There is no right way of drawing up such lists.  By confining myself in this way, Green prospects in seats like Cambridge, Plymouth Sutton & Devonport and Portsmouth South are excluded, though the swings that they require are considerably lower than the swings in most of the seats on this list.)  Anyway, here's the table:

https://drive.google.com/file/d/0Bygi8eZw-4q1dG44RjgyaU4tQkE/view?usp=sharing

This is a daunting prospect for the Greens.  A uniform 15% swing would bring them just five seats from this target list.  A uniform 5% swing (which in itself is a fairly chunky swing) would get them just one seat.

Once again, it needs to be noted that we may well get boundary changes in this Parliament, so this list should not be taken too seriously.  We should be looking at this list as a general indication of where and how the Greens should be focussing in 2020, not as a precise list of named target constituencies.

The south west

The list is illuminating, however.  Three of the top four are Bristol West, Bristol South and Bath. Bristol East, while having a lower Green vote share than the top 30 targets (it's the constituency with the 32nd highest Green vote share), also requires more a modest swing than most on the top 30 list.  A Green focus on this area is automatic.

While most of these seats are currently Labour-held, organising them by reference to swing rather than Green vote share results in the six Conservative-held seats all rising to the top half of the table.  This reflects the fact that these seats have more parties contesting them;  for example, the Greens are in fifth in Truro & Falmouth but it is their seventh most promising seat in their top 30 vote shares as measured by swing required.  The south west is shaping up for a big battle on the progressive side to see who can establish themselves as the primary challenger to the Conservatives.  The Greens are reasonably well placed for this battle if they focus on it.  Will they?

Inner city London

The bottom end of the table is dominated by those inner city London seats.  If the Greens are to make progress here, they need to pull off the same trick that the SNP managed in Scotland - persuading the traditional Labour vote to defect en masse.  Right now that doesn't look remotely likely.  But those London activists will want something to do, so it's more likely than not that the Greens will pour their energies into what looks like a futile endeavour because it's more popular with a large part of its membership.

If the Greens are to try hard to break through in inner city London, they need to consider carefully what their pitch is to the typical Labour supporter in such seats.  It will not be enough to win over right-on urban professionals: the Greens will need a persuasive pitch to the urban poor as well.  They haven't managed that so far, but if the Greens can take the mantle of the anti-austerity party, they may have opportunities.  Much may depend on the Labour party leadership election and the fall-out from that.

Student constituencies

The decisions for the Greens in student constituencies are more straightforward.  They need to embed themselves into student life and make themselves the default progressive choice.  With the implosion of the Lib Dems and the vagueness of Labour's anti-austerity credentials to date, the Greens have made headway.  Labour look set to head further rightwards following their leadership election, so the opportunities for the Greens may well improve further this Parliament.

Summary

It would be surprising if the Greens were able to make a big breakthrough in 2020.  They have too much ground to cover and they can hope to make sizeable gains only if Labour donates them its left wing.  That is unlikely.

But the Greens do have opportunities to progress further.  In the south west they should be fighting hard to become the single biggest progressive party and right now that battle looks well worth fighting.  More widely, they can appeal to the anti-austerity left to pick up support on university campuses.

With its army of members, the Greens could step forward in 2020 - but only if they focus on the task at hand.