I can’t remember a by-election which was so hard fought and was more difficult to call than this one, apart, possibly from Crewe & Nantwich. However, in that one there was no national overhang on a particular party, and there was a definite feeling of Tory momentum. There isn’t in Eastleigh, despite the constituency being flooded with Tory activists and MPs. With the background of the Chris Huhne/Vicky Pryce court case and the media scrum over Lord Rennard, and only a 4,000 majority to overcome. the Tories should be walking this by-election. But they’re not. Question marks over the candidate and the rise of UKIP have both influenced a stalling of the Tory campaign, with the latter proving particularly significant. It would be ironic indeed if UKIP were to be largely responsible for the election of a europhile Liberal Democrat. If that happens, the consequences for David Cameron could be seismic. The media would interpret it as further proof that Cameron can’t win an overall majority in 2015. What will be the reaction of Tory backbenchers and the wider Tory Party? They will be like a dog with a Peter Bone…

For the Liberal Democrats the result is no less important. If they win they will be encouraged to think they can avoid the wipeout most of thing they will suffer in 2015. It will indeed have been a triumph to win in these circumstances, although they would have UKIP to thank, rather than their own very mediocre candidate. But they have fought a good ground war and may yet reap the reward. If they don’t win, the vultures could well start circling around Nick Clegg. Party activists are already horrified by his handling of the Rennard affair. A loss in Eastleigh could provoke open calls for Clegg to go – and not just from Lembit Opik.

Labour has escaped the spotlight in the by-election, which is very odd. They used to have a solid vote in Eastleigh and the demographics indicate that they could have done a lot better here. When John O’Farrell was selected, I wondered if it had been a masterstroke, but in reality he has been a bit of a disaster. Playing the fool does not win votes. The LibDems have squeezed the Labour vote since 1992 to a point where it is only 10%, and it is unlikely they will improve on that tomorrow. Labour need to do much better to break through in the south of England to win in 2015. They will never win a seat like this, but their vote ought to be going up by quite a lot. Miliband will probably escape much scrutiny whatever happens on Thursday, but unfairly.

UKIP will be kicking themselves. John Rentoul thinks they will come second, which is a very brave prediction. If they do, they will wonder what if. What would have happened if Nigel Farage had stood himself? He might as well have done as he seems to be permanently in the constituency. It seems certain they will poll well over 20%, which almost certainly will cost the Tories a much needed win.

So far as I can see, very few people have made a prediction about the result tomorrow, so let me break ranks and call it for the LibDems on the basis that UKIP’s performance has made a Tory victory all the more difficult. A portent of things to come, maybe, with massive possible consequences for David Cameron’s leadership of the Conservative Party.