John Rentoul: Cameron is leaving Brown to hang himself – but must show what he'd do instead

David Cameron is the new Napoleon. We have this on the authority of no less than Bruce Anderson on these pages. Of the present leader of the opposition, Anderson wrote in The Independent two years ago: "No politician since Napoleon has had such a dramatic impact so quickly."

Anderson is right, at least in this sense. Cameron has learnt one of Bonaparte's injunctions very well: "Never interrupt your opponent when he is making a mistake." Not that the Prime Minister has made a mistake, of course. Gordon Brown was happy to clarify that in the House of Commons yesterday. On the 10p income tax rate: "We should have done things better," he said. Now he mentions it, Napoleon's words have been mistranslated. What he actually said was: "Never interrupt your opponent when he is not doing things better."

The point is that Cameron has learnt this lesson well, probably by the use of synthetic phonics and whole-class teaching. Throughout the whole 10p battle, he refused to interrupt Brown by setting out what the Conservatives would do about the problem. He brushed aside the suggestion that it would be more prime ministerial if he were to set out what he thought should be done and how it should be paid for. He thought it should be a matter of changing tax allowances rather than fiddling with tax credits. "But our team is four people rather than the 3,000 the Government have," is what I am told he said to his inner circle.

Now that we have seen what the Treasury's finest have come up with, there was some wisdom in the young leader's approach. Imagine the artificial anger of the ministerial counter-attack if, early last month, Cameron and George Osborne, his shadow Chancellor, had suggested an income tax cut for everyone on the basic rate to be paid for by borrowing. As it is, simple-minded right-wingers are jubilant in welcoming sarcastically the Government's "upfront, uncosted tax cut", which is a jibe at the Cameron-Osborne strategy of refusing to make any such promise.

That is a small price to pay, but yesterday Cameron had to pay a higher price, which was that he was left with little to say. In fact, because he did not want to say whether he was for or against the tax change, he was left with nothing to say at all. His attempt to link his questions to the Prime Minister with the refrain that Brown had failed to be "straight with people" sounded like an essay in search of a theme, written by a student who had failed to stay up the night before in the belief that he could wing it in the morning.

As I say, there is some wisdom in this approach. The 10p tax problem was not of the Opposition's making. It was the most serious of a number of misjudgements made by Brown which hurt him because he tried to be too clever. Brown thought he had got one over on the Tories with his over-hasty attempt to reach the 20p basic rate that the Thatcherites had always wanted. Brown also thought he had scored when he stole the Tory plan to cut inheritance tax, but it did him no good. Recently, he and Wendy Alexander, the Labour leader in the Scottish Parliament, discussed getting one over Alex Salmond, the uppity first minister in Edinburgh, by calling his bluff and challenging him to "bring on" a referendum on independence.

There is a pattern here. People don't mind their politicians being clever and a little sneaky; in fact they expect it, and even admire it, as Salmond has proved. Harold Wilson's devious manoeuvres were indulgently praised before they were despised. As were Blair's blue-eyed "who, me?" moments. But if you are going to be clever, you have got to get it right. That is where Brown has come repeatedly unstuck.

Now Alistair Darling has done the best that could be done to undo the mistake – sorry, the failure to do things better – without actually returning to last year's income tax structure and going back to a 22p basic rate. The most sensible thing to do might be grudgingly to accept that this is the least-worst way of fixing it. Cameron didn't want to do that, for his own rather obviously calculated reasons.

That is where I think Cameron has learnt the wrong lesson from Napoleon. Of course, the Tories should not be trying to interrupt their enemy when he is making a mistake. No doubt that is why they kept quiet about the abolition of the 10p rate at the time, leaving it to the Liberal Democrats and – clever decoy, this – John Redwood to point it out, thus ensuring that the press ignored it until a year later.

However, the Tories certainly ought to be harrying their enemy with helpful suggestions when he is in the middle of trying to put the mistake right. It is all very well claiming that much of yesterday's draft Queen's Speech was copied from the Opposition, as Cameron did yesterday. He quoted some unfortunate minister's description of the plan to elect police commissioners as "completely daft", and said: "I think they meant completely draft." Actually, by doing that he drew attention to one of the few measures in the list that was not a reheat, a theft from the other side or a really bad idea.

The plan for new rights in the workplace is one of the few practical measures proposed since Brown became Prime Minister that might actually make lives better for people – and, because the rights are only the "right to request", they are not too burdensome on employers.

But Cameron's attempt to claim credit for other ideas in the list of draft Bills was undermined by his refusal to engage with the 10p tax issue. Brown's neck turned to solid brass when he said of the Tories: "They have never at any time said that their priority is the low paid and the poorest members of our society." One of the explicit claims of Cameron's statement of values, which his party members endorsed in a ballot, was: "The right test for our policies is how they help the most disadvantaged in society, not the rich."

That was a test that Cameron failed, because he did not come up with any policies to help the losers from the abolition of the 10p tax rate. He and the Tory modernisers say the right things, but they have not backed them up with the hard policy work that is required. Labour's record on poverty has its flaws, which Cameron is sharp enough to identify. But he hasn't yet proposed an alternative approach. Until he does, he will make the Napoleonic error of failing to interrupt his enemy when his enemy is putting things right.

John Rentoul is chief political commentator for The Independent on Sunday

j.rentoul@independent.co.uk