Oops! Three Ashcroft polls are wrong – and Clegg is the loser

Three highly significant polls carried out in the constituencies being fought by Ed Miliband, Nick Clegg and Nigel Farage turn out to be based on bad data.

Corrections issued yesterday by Lord Ashcroft, who commissoned the polls in mid-November, are good news for Miliband and Farage – they’re both doing much better than originally suggested - but bad news for Clegg, who really does face the possibility of losing his seat.

An embarrassed Ashcroft wrote: “Earlier this week, it came to light that a poll I published last November in Sheffield Hallam included a mistake in the data. Concerned that this may not have been an isolated incident, I reviewed two other polls I commissioned from the same company at the same time. As I feared, the mistakes had been repeated.”

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The polls have now been corrected, said Ashcroft, and here’s the upshot:

Sheffield Hallam: Nick Clegg was originally given a three-point lead over the Labour candidate: the polling should have put him three points behind (Lab 30%, Lib Dems 27%, Con 19%, Ukip 13%, Greens 10%). This is significant, because it makes the Ashcroft result a little closer to last week’s polling in Sheffield Hallam by Survation, which showed Labour ahead and which Clegg dismissed as “utter bilge”.

Thanet South: In the Kent seat where Ukip leader Nigel Farage is standing, Ashcroft’s polling showed him trailing the Conservative candidate by five points: it should have shown a much tighter race, with Farage only a single point behind the Tory in a three-way marginal (Con 33%, Ukip 32%, Lab 26%, Lib Dems 4%, Greens 3%).

Doncaster North: Ed Miliband was given only a 12-point lead over his Ukip challenger (a weak position given his huge majority in 2010): Miliband should have been given a safe-as-houses 30-point lead over Ukip (Lab 55%, Ukip 25%, Con 13%, Lib Dems 4%, Greens 2%).

Apologising for the errors, Ashcroft, who employs a number of different polling firms to conduct his surveys, explained that all three polls were carried out by the same firm. He won’t name them - but he won’t use them again, either.

Ashcroft's embarrassment is evident. He fears that the mistakes will cast doubt on his other 100-or-so polls, the most recent being a batch of 18 constituency polls from Scotland showing the SNP likely to wipe out both Labour and the Lib Dems north of the border.

So, should he be worried that we will no longer trust any of his polls? I don’t think so.

All but the most curmudgeonly among politicians, pundits and poll-watchers recognise that the £2 million or so he is estimated to have spent on his marginal constituency polls has added greatly to the public understanding of the political process.

Also, all the data from his polls is in the public domain – unlike the welter of private polling commissioned by the major parties – and is subject to "peer review" by other pollsters and forecasters.

The fact that he is taking the trouble to re-examine his results, and that he quickly confessed to these mistakes will, I think, ensure that most observers forgive him.