In announcing on ITV's Daybreak this morning that he will attempt to force a Commons vote on a Leveson inquiry for the banks, Ed Miliband is repeating the trick that has worked so well him for in the past. It was the threat of a vote that prompted News Corp to abandon its BSkyB bid and that led RBS boss Stephen Hester to relinquish his bonus. Labour will table an amendment to the Financial Services Bill, which is at committee stage in the House of Lords, calling for a public inquiry.

So far, the Tories and the Lib Dems have set themselves against one but Miliband can count on the support of a significant number of their MPs and much of the press, including the Daily Mail. In a leader in today's paper, the Mail declares:

Barclays chairman Marcus Agius is expected to quit today, increasing pressure on chief executive Bob Diamond to do the same. But even that wouldn’t come close to lancing the boil. Doesn’t this latest sorry mess underline still more starkly the need for a Leveson-style inquiry into the whole banking industry?

Both Cameron and Clegg are resisting an inquiry on the grounds that it would slow down any police investigation but this fallacious argument was also used against Leveson. In his article for the Observer, Vince Cable wrote that a "costly Leveson-style public inquiry" (the Leveson inquiry is expected to cost £6m, a meaningless sum when the government spends more than a £700bn a year) would "certainly be enlivened by Ed Balls explaining why, in government, he allowed the regulatory mess to occur in the first place." Indeed it would. Is this not an argument for, rather than against an inquiry?

The longer Cameron resists demands for an inquiry, the greater the suspicion (for right or wrong) will be that he has "something to hide". If he is to tackle the public perception that the Tories are in cahoots with the banks, the pressure to act could become irresistible.