David Cameron said sorry last week. His apology was refreshing, human – and completely calculating. It was designed to make Gordon Brown look as if he were continuing woodenly to deny the obvious. It was designed further to needle the Prime Minister, who, it is reported, became heated on this point with journalists on the plane to his meeting with President Barack Obama.

"What is it you think I should be apologising for?" Mr Brown is said to have demanded. "You don't understand it."

On this, Mr Brown deserves more support than he is given. The game of "say sorry" is one of the sillier devices used by the journalistic trade in its moments of herd mentality. Synthetic and insincere expressions of contrition do nothing to help understand the mistakes of the past, however much leading articles and pundits might declare that mistakes need to be acknowledged before they can be rectified.

And Mr Brown has admitted that mistakes were made, although he is choosy as to what some of those mistakes might have been. He does not accept, for instance, that the system of financial regulation that he set up when he made the Bank of England independent was structurally flawed. Most people differ, although it is difficult to know how much difference an alternative system would have made – a few billions at the margins, probably. And he cannot bring himself to admit that the promise to end boom and bust was a foolish phrase.

The serious question, however, is whether Mr Brown or Mr Cameron have the right policies to get unemployment and public debt back down again. Learning the lessons for banking regulation in order to mitigate the effects of future credit crunches is, frankly, a second- or third-order issue.

On this, Mr Cameron's apology offers us nothing. Last week he said sorry for failing to "say more about banking debt and corporate debt" before the crash. Well, it may be galling to him that Vince Cable, the Liberal Democrat Treasury spokesman, got it right and gained credibility as a result. But it has little bearing on the quality of policy for the future.

More relevant was Mr Cameron's first attempt to apologise, back in January. That was when the BBC interviewed him in his home, and the line to the studio went down just as he said: "I think I have made mistakes." When the line was restored he joked that the interruption was not caused by "one of my press officers outside chopping the cable at the key moment". The mistake to which he confessed on that occasion was his failure to see "just how unaffordable Labour's spending plans are".

That is the key point for the future, on the assumption that the bottom of the current downturn will have been reached in the months between now and the election. The question then ought to be: who will tell the truth about the tax rises and the spending cuts that will be needed to put the public finances back on a sustainable footing?

Politically, and whatever one thought of Tony Blair, the appearance of conversational honesty on television is a priceless asset. Mr Cameron reinforced his advantage over Mr Brown in this respect last week. It was clever to talk of his part in a "cosy economic consensus" which included this newspaper and just about everyone else in the country, with the exception of Mr Cable. But the Tory leader came no closer to spelling out the hard times ahead. And his positioning concealed how little he has to say about the present policy debate, which is focused on the G20 and Budget next month.

Yesterday's G20 pre-meeting did not go particularly well for the Government. Alistair Darling's efforts to reach agreement with other finance ministers in a West Sussex hotel were overshadowed by a news conference in Downing Street. Angela Merkel, the German leader, pointedly said that a further fiscal stimulus had to wait until we saw how the existing stimulus had worked. That was not what Mr Brown, standing next to her, wanted to hear in his earpiece from the simultaneous translator.

On this the Conservatives have little to say. They are sceptical about the VAT cut stimulus but are sensitive to the charge of wanting to "do nothing". Perhaps they can get away with "say nothing" – except sorry – for now, but they cannot escape hard choices for long.

Mr Cameron's apology underscores the electoral threat to Mr Brown's Government. But it takes the Conservatives no further on in setting out how they would deal with the five years after the next 14 months, in which taxes will have to be raised and public spending cut. Mr Cameron does not want to say either of those, so he has come up with the easiest word instead.