This was always going to be a fascinating by-election but tonight’s selection of John O’Farrell as the Labour candidate could make it even more interesting. My suspicion is that he could well attract not just LibDem votes but also a few Tory ones too. He’s a bit of a name, but is the sort of Labour candidate that doesn’t frighten the horses. He looks a bit like a Tory and can sound like one. If he runs an insurgent campaign he could do very well indeed. The LibDems will be more concerned tonight than they will admit.

They will also be monitoring the amount of media attention devoted to O’Farrell. There will be a temptation for much of the media to give him far more attention than Labour’s 13% poll rating deserves. There will also be many editors who would like nothing better to cultivate O’Farrell and promote a surprise Labour win. Not because they are biased towards Labour but because it would be a great political story. The tectonic plates would have shifted.

This by-election is very difficult to call. My instinct tells me the Conservatives have most to lose here. If they don’t win there will be any who see it as a sign that the next election will be out of reach. If the LibDems don’t win, some will take it as a sign of their impending implosion, but they would try to downplay it and blame it on Chris Huhne. Unlike others I’m happy to put my neck on the block and predict a narrow Tory win. That’ scuppered their chances!

More worryingly for David Cameron will be today’s ICM poll which shows that 51% of women intend voting Labour and only 25% Conservative. It really is unthinkable that the Tories could win if those figures stay unchanged. For whatever reason – and we can all think of some – women seem to have fallen out of love with the Prime Minister. He’d better start addressing this problem urgently. But how?