Gordon Brown has made an impressive start as prime minister, establishing a seven point lead over the Tories in an ICM poll last weekend. In Thursday’s by-election in Ealing, David Cameron, the Conservative leader, needs to look like a man who can stop the rot and demonstrate that the “Brown bounce” will not flatten the Tories all together.

Some of Mr Cameron’s critics would go further than this. They would argue that the Ealing by-election is also a test of the Tory leader’s judgment. In recent days, Mr Cameron has invested considerable personal authority in the outcome of the Ealing contest, visiting the constituency five times. The Tories should therefore expect to secure a decent result – coming no worse than second, ahead of the Liberal Democrats and halving Labour’s 11,440 majority. If Mr Cameron achieves that, his decision to train such a strong focus on Ealing will be vindicated.