But how much can we trust single constituency polls?

According to Iain Dale an ICM poll of 1000 voters in Crewe & Nantwich is suggesting that the Tories are on target for their first by-election gain since 1982. The figures are:- CON 43% Lab 39%: LD 16%

Clearly this is a very good pointer for Cameron’s party and the real significance is that it is his party, and not the traditional by election Kings, the Lib Dems who are seen as the party that can take the seat from Labour. If the Lib Dem share had been a bit higher then they could have made the case to Labour supporters that they were the best route to stop the Tories. This poll will put the mockers on that.

A note of caution. As has repeatedly been said here single constituency polls have a reputation of being highly unreliable. In September 2004 NOP has Labour a massive 33% ahead in Hartlepool – the winning margin ended up at 7%. And last year a poll agead of the Gwent by election has Labour comfortably winning back the seat from the independent. The party failed.

The fact that this is ICM gives a good degree of comfort and my view is that the Tories are at least 90% certain to secure comfortable victory.

To another question about how those sampled would vote in a general election the response was the response was: CON 49% Lab 33%: LD 15%.

These general election numbers are sensational. Crewe and Nantwich is listed as the Tories 165th target seat. So for a poll to be suggesting a margin as big as this indicates a Tory landslide and, in many way, supports the latest YouGov national voting intention poll.

Latest by election betting.

UPDATE – There’s an intriguing point in Iain Dale’s report – He says:“I am told the by election figures were adjusted downwards to take account of large number of Labour don’t knows. If they stayed at home on polling day, the Tories would win by 13 points.”

We desperately need to see the details but this might explain the disparity between the by-election figures and those for the general election.

If you tell ICM that you will vote but that you don’t know who that will be for the pollster assumes that 50% will go in line with what they did last time. This is known as the “spiral of silence adjustment”. My guess is that a very large number of 2005 Labour voters answered don’t know and this is what makes up the 13%.

Whatever this poll is very good news for the Tories.

Mike Smithson