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.

The data has now been corrected, and the upshot is that, in Sheffield Hallam, rather than having a three-point lead, Nick Clegg should have been three points behind Labour:

Labour 30 per cent, Liberal Democrats 27 per cent, Conservatives 19 per cent, UKIP 13 per cent, Greens 10 per cent.

In Thanet South, rather than a five-point Conservative lead, the poll should have shown a very tight race with UKIP’s Nigel Farage:

Conservatives 33 per cent, UKIP 32 per cent, Labour 26 per cent, LibDems 4 per cent, Greens 3 per cent.

And in Doncaster North, Ed Miliband is a full 30 points clear of his nearest challenger:

Labour 55 per cent, UKIP 25 per cent, Conservatives 13 per cent, LibDems 4 per cent, Greens 2 per cent.

The results have been updated on the Constituency Polls section of my website, and the corrected data tables for Hallam, Thanet and Doncaster are also on my site.

I have not been in the habit of naming the polling companies I use, all of which are members of the British Polling Council, and I will not be naming this one. But I cannot allow this episode to cast doubt on the reliability of my polling more generally.

So I must disclose that these three surveys last November are the first and only I have commissioned from a well-known but relatively new polling firm. And no, I won’t be using them again.

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