Friday, 16 January 2015

Reality check: testing the betting markets against external data

Up to now I have been working on the basis that the various betting markets on politics reflect the balance of opinion among those who are willing to place money on the outcome, and thus represent the current conventional wisdom about what is most likely to happen.  But that begs the question who are these people who are willing to place money on political bets.  Are their instincts skewed in any ways?

I do not have inside information on those who actually place bets on the political markets, but we can make deductions from the prices as to what motivates them to bet.  So let's look at one set of constituency markets.

A straight choice

To make it easy, I'm going to focus just on the Conservative-held seats that are Labour targets.  I'm going to exclude all seats where any other party is priced at 5/1 or less (or shorter than Labour), to cut out triangular fights.  That leaves 91 of Labour's first 125 targets.  Here they are arranged in order of swing required for Labour to take them:

The first thing to notice is that the prices are driven by considerably more than swing.  The first seat on the list, North Warwickshire, is rated by punters as a less likely Labour gain than the 23rd seat (Brentford & Isleworth).  The 87th seat on the list, Portsmouth North, is rated a more likely Labour gain than the 50th seat, Vale of Glamorgan.  There is clearly a correlation with swing, but it's far from perfect.

Swing vs odds

Let's look at these seats reorganised by odds (I've used the Conservative prices):

I've also changed the numbering so I you can easily see the movements between these two lists.  On average, there is a difference of over six places for each seat between these two lists.  Note, I have deliberately constructed a set of comparable seats with minimal third party interference (Dudley South, Crawley and Brigg & Goole being the only seats on the list where any other party is significantly affecting the two main parties' odds).  Yet punters seem sure that uniform national swing is going to be varied from fairly markedly even within this most typical of sets of seats.

19 seats shift 10 or more places, as follows:

20 or more places

Portsmouth North
Stockton South
Enfield North

15 or more places 

Dudley South
Calder Valley
Morecambe & Lunesdale
Ealing Central & Acton
Bristol North West

10 or more places

Plymouth Sutton & Devonport
Brentford & Isleworth
Preseli Pembrokeshire
Milton Keynes South

The bigger the shift, the more compelling a reason we should be looking for to justify that shift.  In some cases, the reason will become apparent.  In others, I can't see why there are such big movements.

Uniform national swing

Leaving aside the internal movements, let's think further about the implications of uniform national swing.  In the last few YouGov polls, Labour have posted 33% (give or take a point either way) and the Conservatives have posted 32%.  That is a swing across the UK of 4%.  That would mean that Labour could reasonably expect to take every seat up to Stevenage, the 47th seat on the list.  But Labour are in fact odds against or second favourite  in every seat bar one after Keighley, the 39th seat on this list, where only a swing of 3.1% is required.

If that is true of national swing, it is still more true of the position discounting Scotland.  Labour are racking up a swing against the Conservatives of 5% or more outside Scotland, suggesting still greater gains.  Evidently this does not faze punters on the constituency markets. 

And all this is minor compared with the "most seats" markets.  On Betfair, Labour and Conservative are both just about evens to get most seats.  This implies a swing to Labour in these constituencies of under 2%, even allowing for the SNP taking a big bite out of Labour's Scottish seats.  If you take this view of affairs, you should instead be betting on the Conservatives at odds against on the constituency markets in seats like Hastings & Rye and Nuneaton.

Clearly punters are expecting the swing to Labour to subside a bit from present levels.  You need to decide for yourself whether that is reasonable.


Geography is destiny, so they say, but punters don't seem convinced.  These 91 seats are spread across nine regions: there are no Scottish seats.  If we leave the one seat in the north east to one side as representing too small a sample (I will not be expecting a major Conservative renaissance in the north east on the basis of Stockton South), the regional pattern is quite muted.  In London and the South East, the Conservatives are rated by punters at 3.6 and 3.7 places per seat worse than uniform national swing would suggest.  In Wales, the Conservatives are rated by punters at 2.5 places per seat better than uniform national swing would suggest and in the East the Conservatives are rated by punters at 3 places per seat better than uniform national swing would suggest.  But otherwise, the effects of geography aren't worth noting.  I should record that the result in the South East is almost entirely attributable to one seat: Portsmouth North (and that we would see the Conservatives rated at 3.7 places per seat better in the West Midlands than uniform national swing would suggest if the unusual seat of Dudley South is excluded).

I think that punters are probably underestimating the effects of geography at the next election.  In particular, as we shall see, there is quite a bit of evidence that Labour are outperforming in London and I'm not convinced that this is adequately reflected in the markets yet.


Unlike previous general elections, we have had a plethora of constituency opinion polls, particularly for this section of constituencies.  Survation have polled in Stockton South and Crewe & Nantwich, while Lord Ashcroft has polled in no fewer than 50 of these seats.  Both Lord Ashcroft and Survation stress that opinion polls are snapshots not predictions, but in the absence of more direct methods of getting information for predictions, opinion polls are inevitably going to be used to some extent to help punters make predictions.

Here are all the polls for constituencies on this list, in decreasing order of Labour lead:

I've also included a column in the table of seats organised by odds (in the link given further up) which includes the headline poll figure.

Only 11 of Lord Ashcroft's constituency polls show a lead for the Conservatives, and only one of the Survation polls.  But punters don't really seem to be taking all that much notice of these constituency polls.  Only 12 of the constituencies noted above that have moved ten or more places out of order from uniform national swing on the odds table have constituency polls.  Labour are shown just on the seats polled to be presently ready to take 40 of the 51 seats polled.  Either the punters don't believe the polls or they are expecting swingback to the Conservatives.

As can be seen from the table above, there are some anomalies.  The Conservatives are rated less likely to take Hove than Carlisle, despite recording only a 3% deficit in Hove and an 11% deficit in Carlisle.  The Survation poll in Crewe & Nantwich seems to have been essentially ignored.

Should punters be taking more notice of the constituency polls?  It's hard to know how much weight to put on them, because in Britain we have limited experience of their use and this has been drastically increased in advance of this election.  I have reservations about them, since they involve the compilation of non-standard polling bases for each constituency.  The risk of mistakes is much greater and there is always the risk that a poll in a particular constituency is an outlier.  A surprising result may just be a quirky sample - these things are to be expected from time to time.

But having disparaged them, I also recognise that they are the best information that we have in most seats.  We ignore them at our peril.

How best to use them?  It would be unwise to rely on single polls uncritically.  Where we have more than one poll in a single constituency, as in Stockton South, we can be much more confident about the underlying picture.  Unfortunately, that is the extent of the seats on this list with two polls.

As with any opinion poll, the headline figure of each poll should be treated as in the rough area of the actual lead.  So a finding of a 5% lead might easily be 2% or 8% - 5% is merely the single most likely lead on the data available.  Where the two parties are found to be dead level, it is equally likely that each was in reality in the lead in the constituency at the time the poll was taken.  But a finding of a 10% lead is unlikely to mask a reality where both parties are neck and neck. 

Again, we should always remember that a poll is a snapshot not a prediction.  Things may change.

I am more confident when we can look at comparable constituencies together.  So with that in mind, I have prepared a list of the seats by region:

In the north west, the Conservatives are apparently outperforming in both Morecambe & Lunesdale and Blackpool North & Cleveleys, given the size of their majorities in those seats.  The fact that we have two Lancashire coastal constituencies telling the same story strengthens the credibility of both polls.  We don't have a poll yet for South Ribble, but might that outperformance extend down the coast?

In the east midlands, punters seem not to believe that Lincoln or Amber Valley are quite close, despite Lord Ashcroft's polls suggesting that the Conservatives are only a bit adrift, apparently relying more on the small swing required to take them.  If you do take the view that the Conservatives might revive a bit against Labour, both of these seats are worth considering for a bet on the Conservatives.

There are substantial swings to Labour in every London Conservative/Labour marginal so far polled except Harrow East.  That makes that particular poll a little suspect in my eyes (particularly since the pattern of a strong Labour performance is also reflected in polls in Hampstead & Kilburn and various Lib Dem/Labour marginals).  At present, neither Finchley & Golders Green nor Enfield Southgate are seen as disproportionately likely to fall to Labour.  If the trend is replicated in those constituencies once polled, the odds on Labour are likely to be cut sharply.  I'm already on Labour in Finchley & Golders Green from last year and I've now invested a small sum in Labour in Enfield Southgate too.

In the west midlands, the Conservatives seem to be bearing up fairly well in general.  The Wolverhampton South West poll will disappoint them, and the poor odds on the blue team in Dudley South reflects an extraordinary poll from Lord Ashcroft in Dudley North which shows UKIP a whisker behind Labour.  But the odds on the Conservatives holding Stourbridge, which is adjacent to Dudley South, have so far been completely unaffected by this deduction.  This may be a seat worth a few quid on Labour too.  But take your own view of the matter - Halesowen & Rowley Regis is adjacent to Stourbridge and the results of Lord Ashcroft's poll in that constituency were pretty good from a Conservative perspective, given the size of their majority.

There have been four polls in the eastern region and all four have been fairly poor for the Conservatives.  However, this does not seem to have been noticed.  Perhaps the betting public assume that East Anglia is predestined to be blue.  None of the prices on the Conservatives look attractive and the evens on Labour in Stevenage still looks decent to me, given that Labour recorded a lead of 5% in a recent poll.

Mysterious seats

Even after taking all these points into consideration, some of the large movements look odd. Why are the Conservatives so poorly thought of in Portsmouth North?  Why are Labour thought so likely to win Bristol North West from third?  Why is Rugby seen as so safe for the Tories?  None of the information available seems strong enough to justify large deviations from the norm.  Betting against these anomalies seems sound.


Punters do seem to be taking a sunnier view of the Conservatives' chances on the betting markets than the current information would suggest if no further polling movements take place, apparently on the assumption that in the run-up to the election, the polls will swing back in the direction of the Tories.  The movement being anticipated is not all that large on the constituency markets, so far as one can judge from the constituency polls so far conducted.  The movement expected on the general "most seats" markets is larger, and must be correspondingly less likely.

Some of the seats seem to be irrationally regarded as safer for the Conservatives than the information available suggests, and some the reverse.  There remain betting opportunities, even in the simpler problems posed by a straight fight between the two main parties.

Thursday, 8 January 2015

Political betting resources

This isn't a particularly interesting post, but I hope it's a fairly useful one.  I've tried to gather together some useful resources sites in one place.  It's an oddity, but it's easy to find lots of opinion sites but rather harder to find the sites that just record the underlying data.  It seems, after all, as if comment is sacred.

I'll try to remember to add to this as and when I come across other useful sites. 

Previous national results

We can't know where we're going unless we know where we're starting from.  Here are the 2010 election results from the BBC on a convenient clickable map:

Here are the Holyrood results from 2011:

And the Wales results from the same year:

Finally, and critically for Scotland, the results of the independence referendum in detail:

Local election results in this Parliament

Personally, I'm not too fussed about local election results, but here they are for 2011, 2012, 2013 and 2014:

And this might prove useful when assessing UKIP prospects:

European election results

We shouldn't forget the Euro election results from 2014 either.  Again, I think that they can be overinterpreted, but they do have their uses:

These can be found in detail by council for most regions as follows:

Overall (but some of the links on this page are dodgy):

South West

South East

East of England

West Midlands

East Midlands


North East



Seat guides

Next we need to know the battlegrounds.  For this, UK Polling Report is indispensible:

Wikipedia is better for getting turnout numbers quickly though, and sometimes has more detail on the composition of the seat.

We've had this leaked list of seats that the Conservatives are supposedly not targeting:

I have my doubts about how accurate it is, but it's worth looking at.


It's always good to know something about the candidates.  AndyJS has put together a fantastic, fully comprehensive database for this:

And GE2015 has given some background on the UKIP candidates in the most winnable seats:

It's always worth doing a quick google on any candidate you're thinking of backing.  Some have quite colourful histories.  Others (unfortunately, a smaller number) have inspiring pasts.  Most candidates of major parties have their own websites and many have their own twitter feeds.  If you're backing them in a big way, investigate those too.

Personally, if I were a candidate, I would say as little as possible.  Even a fish wouldn't get caught if it kept its mouth shut and no one ever remembers the brilliant things you say.
National opinion polls

Once again, UK Polling Report is the best hub for national polls:

This is usually a few days out of date, but the main site updates on the most recent polls.

In Scotland, John Curtice's site is the best resource on polls.  Here's a link to the Westminster 2015 polls:

And in Wales the polls are gathered here:

There are also some London-only polls, but these do not seem to be conveniently collected together in one place.

Constituency polls

This time around, we have a lot of constituency polls.  Lord Ashcroft's are conveniently compiled here:

May 2015 present them on a map rather than alphabetically here:

Here are all the constituency polls of pure Labour/Conservative marginals, arranged in decreasing order of Labour lead:

Survation have also compiled quite a few constituency polls too, though these aren't as conveniently presented.

South Thanet:


Grimsby and Dudley North:

Folkestone & Hythe, Bognor Regis & Littlehampton, Great Yarmouth and Crewe & Nantwich:

Rotherham, North Thanet and Boston & Skegness:

Stockton South:

ICM also conducted six controversial opinion polls - 

In Cambridge, Sheffield Hallam, Wells and Redcar:


and Inverness, Nairn, Badenoch & Strathspey:

Lord Ashcroft has now produced his Scottish constituency polls, and his commentary on these should also be read carefully:

Seat calculators

We have a few different seat calculators and everyone has their own secret sauce.  I have my doubts about how useful they will be in an election where so much has changed since 2010, but they're always a good sense check on any prediction.  Have fun:

Betting sites

Now finally, to betting.

Oddschecker is an essential starting point, listing best prices on every market it can get its hands on:

It's not 100% reliable though, so it's worth double checking on its prices sometimes.  And not all bets get to it (thanks to the labyrinthine nature of some of the bookies' websites, I think).  Sometimes it's messed up by identical bets being expressed differently by different bookies, so look at them carefully.  Sometimes it's messed up by spelling mistakes in constituency names by the bookies.  So don't rely on it completely blindly.

I'm not going to link to all markets, so you'll have to navigate your way around the bookies' websites for yourself, which is easier said than done in some cases.  However, I've made an exception for the constituency markets, because it's handy to be able to look at all of them together.

Here's a direct link to the Ladbrokes constituency markets:

Those for Paddy Power:

And those for William Hill:

With the election coming, I expect we'll see seats again from Stan James and perhaps Coral and Sky Bet (which offers a bet on Rochester & Strood at present, but nowhere else so far).  Others may venture into the arena too.

And if you go in for spread betting, here's a link to the Sporting Index political bets:

Good luck.

Tuesday, 6 January 2015

Bedtime stories: extending my thoughts about Scottish constituencies

Always beware of a bright idea.  As I explained in my last post, I've been thinking about how the referendum may play out in individual constituencies.  And once I start worrying at a problem, I can't give up.

To set the scene, let me recap with my last post:

I've been trying to put together a methodology for working out how the rise of the SNP could work through to the May 2015 general election results.  We know that the SNP have risen sharply in the polls.  However, uniform national swing is always dangerous to use when a rise is as sharp as the one that the SNP seem to have got (it is inherently unlikely that a large increase will be uniform) and on this occasion we can be fairly confident that the increase is not uniform, because it seems to have been driven by the referendum on independence.  Since Yes did much better in some areas than others, we can expect the SNP to be increasing support disproportionately in the areas where Yes did best.

In my last post, I looked just at Glasgow.  I've now tried to produce a means of guessing how each individual constituency might pan out.

Feeling the aura of referendum voters

As I explained last time, my starting point is to look at how we got from the 2010 results to the referendum result.  I decided to proceed as follows with the following very rough and ready assumptions.  

The first critical point was to understand how much of the Yes vote came from the leading unionist party.

I would allocate all the Conservative votes in 2010 to No and all the SNP votes in 2010 to Yes.  Hopefully the exceptions would cancel each other out.

Next, in seats where Labour were ahead of the Lib Dems, I would allocate the 2010 Lib Dem votes 60:40 to No.  Why 60:40?  It's fairly arbitrary - I might have picked 2:1.  Or I might have picked 50:50.  But 60:40 felt right somehow.  (Where the Lib Dems are ahead of Labour, I decided that getting the Lib Dem share right was more critical, so I have assumed that the Labour share was 60:40 to No and sought to work out the Lib Dem proportions of Yes: No.)

As for all the other parties - other than Labour - I decided to treat them as dividing 50:50 between Yes and No.  This is loose - 2010 UKIP supporters were probably disproportionately likely to be No and 2010 Green supporters were probably disproportionately likely to be Yes.  But life is too short.

We next need to recognise that many referendum voters did not vote in 2010.  I decided to allocate these 60:40 to Yes where Yes got over 45%, 50:50 where Yes got between 35 and 45% and 40:60 where Yes got below 35%. The cut-offs and the percentages are arbitrary.  I just chose what seemed like reasonable assumptions that I could work with fairly easily.

That leaves the 2010 Labour voters (or in those few seats where Labour are behind the Lib Dems, the 2010 Lib Dem voters). I could then treat them as making up the balance on each side, knowing the referendum result in each council. 

Applying this "knowledge" to look at voting in individual constituencies

At this point, I now "knew" how the referendum result had been compiled.  What could I do with this "knowledge"?  Time for some more assumptions.

My starting point is that Yes voters who had voted in the 2010 election are very likely now to vote SNP.  I decided that 80% of such voters (whatever party I had deemed them to come from) would vote SNP next year.  That is me putting the zeal of the convert into figures.

Then there is the question of new voters in the referendum.  For some, this will be a habit to be repeated.  Given the superior ground game that the SNP will have (all those extra foot soldiers must be worth something), I have taken the view that previous non-voters who do vote will be disproportionately likely to vote SNP.

I decided that only half of new voters would vote in May, but of those half, they would vote as follows:

Where Yes is above 45%,

In a Labour-held seat:

Labour 30% 
SNP 60%
Others 10%

In a Lib Dem-held seat 

Lib Dem 20% 
Labour 10% 
SNP 60% 
Others 10% 

Where Yes is between 35% and 45%,

In a Labour-held seat 

Labour 40% 
SNP 50% 
Others 10%

In a Lib Dem-held seat 

Lib Dem 25% 
Second unionist party 15%
SNP 50% 
Others 10%

Where Yes is below 35%,

In a Labour-held seat 

Labour 50%
SNP 40%
Others 10%

In a Lib Dem-held seat 

Lib Dem 30%
Second unionist party 20%
SNP 40%
Others 10%

In the one Conservative seat, allocate new voters as follows:

Conservatives 20%
Labour 20% 
SNP 50% 
Others 10%

You will note that I haven't looked at the SNP seats.  With all six at 1/100 shots, I have better things to do with my time.  Sorry about that.
Then there's the question what to do about the Lib Dem collapse in the polls.  I hummed and hawed about this.  In the end, I decided that in seats which the Lib Dems did not hold, they would lose three quarters of their 2010 vote, with Labour, Others and abstentions evenly sharing those votes that were not accounted for by the SNP and the Lib Dems.
In Lib Dem held seats, I needed to something different to reflect the incumbency and the effort that the Lib Dems would put in.  So I replaced the usual assumption that the Lib Dems would lose 75% of their 2010 vote with an assumption that 20% of post-SNP defectors would transfer to Labour, while the remainder remain loyal to the Lib Dems.  In seats where the incumbent is not standing, I upped that percentage from 20% to 35%.

And that's all there is to it.  Except to do the sums.

That's easier said than done.  Some councils exactly match the boundaries of single constituencies.  Some councils have several Westminster constituencies.  Some constituencies straddle two or more councils.  Some councils helpfully gave a lot of detail on their referendum results, while others have been much terser.

How did I deal with this?  Well, when I came across a problem, I just took a view and either approximated using the council that seemed most appropriate or used something that looked close to an average between the relevant councils.  Or I did the calculation on two bases (fortunately each time I did this the result was in the same ballpark).  I went below council level where I could match up referendum results with the constituency, as in Edinburgh, but I didn't when the council reported on a different basis, as in Glasgow.  I didn't have time.  Go ahead if you feel like it.

Why have I spent so much time explaining this?
Because I don't want you treating this with any kind of reverence or thinking that I am impressed with my own efforts.  The intention is to produce an extremely rough and ready artist's impression of what Scotland's Westminster seats might look like after May 2015.  It is in no way a prediction (unless it turns out to be right, in which case I shall waste no opportunity to trumpet it).  It's a sense check.

You will no doubt disagree with many or even most of my assumptions.  Go ahead.  The idea is to set down an idea to kick around.  I have no illusions that this is some kind of work of genius.

I'm refusing to give precise figures.  I don't want anyone to get any spurious idea of precision about this.

Opening the envelope

So, here goes.  The headline figures are:

Labour: 15
SNP: 40
Conservatives: 3
Lib Dems: 1

And here are the constituencies in detail:

In all constituencies that the SNP do not take, they are second unless explicitly stated.

For me, though, what's more interesting is to see which seats are most vulnerable to the SNP on this type of model and which are more resistant to their charms.  The SNP would tear through the west coast of Scotland.  But Linlithgow & Falkirk East (currently priced at 5/6 for the SNP) would stay in the red column.

I was kind of expecting the SNP to do well on my model in the northern Lib Dem seats, but I was shocked at just how well they did.  (What's really driving this in my model is the relatively high vote for Yes in Highland (47%) and the high turnout in that council in the referendum relative to the 2010 general election.)  

My model makes no allowance for tactical voting.  Seats like Edinburgh West, Edinburgh North & Leith and Aberdeenshire West & Kincardineshire might very well turn out differently in practice once the campaigners get to work on the electorate.  Aside from the Lib Dems, it makes no allowance for incumbency either.  

Using this table for betting
Please don't.  At least, please don't take it literally.  It's intended to give you something to think about.  It's not a predictor (yes, I know I've said this once, but I want to say it again in case you missed it the first time around).

What it may help with is in spotting hidden opportunities.  Cumbernauld, Kilsyth and Kirkillintoch East was at 2/1 the other day, but since the SNP would take this with some ease on my model, I've had a bet on that.  Note what good value the Glasgow seats look on this model.

This is a model not a prediction
Yes, that's a third time.  But this time I have a slightly different point to make.  Things could change dramatically before May even if this model fitted the current direction of travel quite well.  Nothing is preordained.  Jim Murphy may yet turn things around, though that looks odds against to me.

Incidentally, you can get 5/6 on the SNP taking more than 26 seats with Ladbrokes.  If you have faith in all this.  But as I said at the outset, always beware of a bright idea.

Saturday, 3 January 2015

The SNP conundrum: a Glasgow experiment

Early this morning, I lay awake in bed thinking about Glasgow constituencies.  I appreciate that this is not a conventional thing to do, but that's how I roll. 

The problem

What was troubling me was the difficulty of working out how the rise of the SNP would work through to the May 2015 general election results, so I started thinking about a methodology for dealing with this.  We know that the SNP have risen sharply in the polls.  However, we have no clear idea of how this will play out.  Opinion polls are snapshots and not predictions. 

Uniform national swing is always dangerous to use when a rise is as sharp as the one that the SNP seem to have got (it is inherently unlikely that a large increase will be uniform) and on this occasion we can be fairly confident that the increase is not uniform, because it seems to have been driven by the referendum on independence.  Since Yes did much better in some areas than others, we can expect the SNP to be increasing support disproportionately in the areas where Yes did best.

I'm not the first to have been looking at this problem.  Stephen Bush had a bash in a Telegraph blog here:

And John Curtice has tried interpreting the most recent ICM Scotland opinion poll here:

Getting to Yes

So I started thinking about how I might approach this.  Put bluntly, I decided to make a series of guesses informed by such data as we have.

The great advantage of lying in bed without access to any data is that you can start from first principles without trying to fudge the assumptions to get the answer that you want.  My starting point is to look at how we got from the 2010 results to the referendum result in Glasgow.  I decided to proceed as follows.  I would allocate all the Conservative votes in 2010 to No and all the SNP votes in 2010 to Yes (I appreciate that this is not strictly true in either case, but I'm looking for a rule of thumb - there are more heroic assumptions coming up so I don't need to stress too much about being too accurate).  Next, I would allocate the 2010 Lib Dem votes 60:40 to No.  As for all the other parties other than Labour, I decided to treat them as dividing 50:50 between Yes and No.

We next need to recognise that many referendum voters did not vote in 2010.  I decided to allocate these 60:40 to Yes.  That leaves the 2010 Labour voters, who I decided to treat as making up the balance on each side. 

There are multiple assumptions in this (for example, that departing and dying voters were exactly replaced by new voters).  But it's a start.

Putting theory into practice

How does that work out?  There are seven general election constituencies in Glasgow, and they totalled as follows:

Lab: 128818 (56.2%)
Lib Dem: 31403 (13.7%)
SNP: 39702 (17.3%)
Con: 17482 (7.6%)
Others: 11818 (5.2%)

Total: 229223

Turnout: 54.9%

The referendum results are here:

As you can see, it was a 53.5% Yes vote on a turnout of 75% (so 40.125% Yes, 34.875% No, 25% Didn't Vote).

These two results are not exactly comparable, because the referendum result for Glasgow covered a slightly larger area than the Westminster seats.  But there are plenty more assumptions flying around, so let's use those figures for now.

Using my assumptions above, that gives us a Yes vote comprised as follows:

SNP: 17.3 x 54.9%
Lib Dems: 13.7 x 0.4 x 54.9%
Others: 5.2 x 0.5 x 54.9%
Non-voters: 0.6 x 20.1%

26% Non-Labour voters

So Labour voters: 14.125% (ie 45.8% of 2010 Labour voters)

And a No vote comprised as follows:

Conservative: 7.6 x 54.9%
Lib Dems: 13.7 x 0.6 x 54.9%
Others: 5.2 x 0.5 x 54.9%
Non-voters: 0.4 x 20.1%

18.2% Non-Labour voters

So Labour voters: 16.675% (ie 54.2% of 2010 Labour voters).

Back to bed, back to reality

Now I would like to invite you to return with me to my bed.  Without any knowledge of the above calculation, I then started thinking about how the referendum might affect voting intention.

I started by assuming that 2010 SNP and Conservative voters would each remain loyal to their cause.  I figured that the SNP would pick up 80% of Yes voters who had not previously voted for them but who had voted in previous elections.  I assumed that the Lib Dems would lose three quarters of their vote in total from 2010, and to the extent that it did not go to the SNP that lost vote would be split evenly between Labour, other parties and Don't Vote.  Labour would keep all their 2010 voters who did not defect to the SNP.

What of those who voted only in the referendum?  I figured that the experience of voting might be catching, for some at least.  I guessed that half would vote again in May 2015, and that this would be split 3% Labour, 6% SNP, 1% to others - I gave the SNP a share disproportionate to the Yes vote to reflect its much greater ability to run a ground game.

So let's feed that through into the above figures:

Labour: 37%
SNP: 47.6%
Lib Dems: 3%
Conservatives: 6.5%
Others: 5.9%

Turnout: 63.7%

What does that mean?

If that was indeed the result, it would be carnage for Labour in Glasgow.  There would be a swing of just under 25% from Labour to the SNP in Glasgow.  The only seat that it would retain if the swing was uniform across Glasgow would be Glasgow North East - and that only just.

Meanwhile, the SNP are favourites in only one seat in Glasgow: Glasgow North, and then only at 8/11.  If my guesses are anywhere near right, the SNP would have a majority of 15% or so in Glasgow North.
Can I extend this to other Scottish constituencies?
Well, yes I can, and it will work well in Labour-held constituencies, since these are essentially two body problems.  When I have the time and inclination, I shall do so.

I don't see this technique working as well in Lib Dem or Conservative held seats though.  There are additional variables at play in such seats.

How confident am I in my guesses?

Not very.  But the errors should mostly cancel themselves out.  I've made limited allowance for the SNP's greater ground resources and I've given Labour nearly as big a chunk of former Lib Dems as the SNP.  I've made no allowance for any increase in UKIP tallies, which is far more likely to damage Labour than the SNP.  Set against that, I'm not at all sure how the likely increase in turnout will play out and I've made no allowance for the Greens to get any uplift.  I may have been too assertive in how many former Labour supporters who voted Yes will switch to the SNP but I've made no allowance for any former Labour supporters to drift to abstentions. 

And of course, we may have more events.

For now, however, I'm using these calculations as a rough and ready way of taking the impact of the referendum into account.  It would not stand any kind of academic analysis.  But it will do for now, in the absence of better information.  If you disagree, at least this post may help you make your own assumptions.