Gordon and Dave play the expectations game

Olivia Newton John and John Travolta were in the charts, singing You're the One That I Want from their new film Grease, when the Tories last took a seat off Labour in a parliamentary by-election. It was Ilford North in 1978.

Have New Labour’s fortunes fallen so far that the Tories can pull it off again this week in Crewe and Nantwich? An ICM poll puts the Conservatives eight points ahead of Labour in Crewe, which would translate into a 12 per cent swing to the Tories since the general election; only an eight per cent swing is needed for victory.

So it appears a foregone conclusion. All that remains to be seen is by how much of a margin the Tories can win – and how the two party leaders fare in terms of expectations.

Brown, until this past week, was expected to lose Crewe. If local party workers could

keep the swing to the Tories within single figures, the PM would be able to write the defeat off as a fluke of circumstance and claim his fightback had begun. But that was before he decided to spend £2.7bn on a 'bribe' to dispose of his 10p tax band problem and announce a raft of new Bills designed to persuade us he is back in business and boost party morale.

The paradox is that any optimism could be a trap for Brown. Now a heavy defeat – with a swing to the Tories in double figures - will raise questions among MPs as to whether they need a change of leader before the next general election.

And what of David Cameron? Defeat in Crewe would be a huge blow. Yet he is just as keen as Gordon Brown that Labour shouldn't be crushed, forcing a change of leader. Just as Blair once had William Hague and Iain Duncan Smith to push around, Cameron reckons he has the measure of Brown. He is the man he wants to take on at the next general election.