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Could Cameron really be heading for a 260 seat majority?

One of the things I often write when talking about UK polling is that based on two decades of general elections, every single London mayoral race and every single by election where there has been polling the “golden rule” has applied.

This says simply that the most accurate survey when tested against real votes has been the one that has had Labour in the least favourable position.

So the seat projections above are what happens when you input the overnight poll data into the Anthony Wells seat calculator. The outcome is quite dramatic – a Conservative majority of 260 seats.

The new survey is from Ipsos-MORI – the pollster which set up a major review of its methodology following the London Mayoral result. This took a couple of months and now involves only doing voting intention polls by phone, continuing to report headline figures taking only those certain to vote, and applying special measures to counteract the effect of public sector workers being over-sampled.

The results for August with comparisons on a month ago are: CON 48% (+1): LAB 24% (-3): LD 17% (+2). This is the second biggest lead for the Conservatives in several decades. The biggest, 26%, came in a YouGov poll after the May elections.

The certainty to vote issue is very important – without this filter the pollster would be reporting a Tory lead of 14% based on a split of CON 42% to LAB 28%. MORI always find that Labour do better on this calculation because party supporters have been shown at election after election to be less likely to turnout than Tories.

Arrangements on PB for the next fortnight: I’m off on holiday to the Pyrenees while Morus is heading off to Denver for next week’s Democratic convention. Paul Maggs is not available. So the normal pattern of postings might not operate and there could be longish periods when the moderation box is not cleared. I have a few articles which were “prepared earlier” and we will try to put up continuation threads if discussions get much longer than 500 comments. What a time to be away? I wonder what changes there be in the political world when I return on September 7th?

Coming up on PB: Later today, Obama running mate developments permitting, I will be publishing HenryG Manson’s betting guide on the Scottish Labour leadership contest. His tips might be worth following and there could be money to be made!

Mike Smithson

One thing that Friday’s London mayoral result showed was that I term “The Golden Rule of British Polling” still applied. For based on the results of the last four general elections and all three London Mayoral races the most accurate poll has always been the one showing Labour (Ken in 2000) in the least favourable position in relation to the Tories.

The rule was the key factor that determined my betting in last week’s election and in the end I had considerably more than a month’s after-tax income at risk. But I never had any real doubts that it would come good. If we had taken an average of the polls we would not have been right.

So taking the latest output at any one time of the five major firms carrying out general election voting intention polls – ComRes, ICM, Ipsos-MORI, Populus and YouGov – the numbers from the poll that satisfies the rule will be put into the two major online seat predictors and be published here.

The calculators, from Martin Baxter’s Electoral Calculus site and Anthony Wells’s UKPollingReport have a different mathematical approach. There has been lots of discussion about the way these two work and others have also developed their own models which we might include in the future. They are, of course, just a guide and are less robust than the Golden Rule. I think that they both understate the Lib Dem position.

The central thing here is the input data which will be restricted to the poll showing Labour in the least favourable position.

This is controversial but the Golden Rule has been tested against real results over a long time period and until it is proved wrong it seems the best approach to take.

Mike Smithson