The partial breakdown in the relationship between the Prime Minister and the Chancellor is serious, and damaging both to the Government and the country. On the face of it, it is so remarkable that Tony Blair should have been forced to rebuke his friend and ally in yesterday's newspapers that it is tempting to believe it must be an optical illusion in the world of smoke, mirrors and spin that is modern high politics. But there can be little doubt that Mr Blair wanted it known that he has lost patience with Gordon Brown's "psychological flaws" and his "daft and ill-advised" venture into vanity publishing, to repeat two of the most derogatory phrases attributed yesterday to those speaking on the Prime Minister's behalf.

This is the closest to a public dressing-down that can be administered without actually going public. It followed a pointed reminder to the Cabinet last week of the virtues of unity, and the announcement that Mr Blair would himself take the chair of a new welfare reform committee, with Deputy Prime Minister John Prescott, rather than the Chancellor, filling in in his absence.

It says a great deal about the state of the relationship between Nos 10 and 11 Downing Street that Mr Blair should have calculated that it was better to expose division at the heart of government than to allow Mr Brown's blatant self-promotion to go unchallenged.

Arguments over the busy buzzing of Mr Brown's supporters may seem like the small change of politics. Individually, the charges laid against the Chancellor by the Blairites are petty. He allowed a television documentary to be made about his role in Labour's election victory. He let it be known that he regarded himself as prime minister to "president" Blair: while the sweet phrases came from No 10, the serious action came from No 11. And he chose to "co-operate" with Paul Routledge over his biography, which laid bare his continuing resentment over the Labour leadership contest of 1994.

It was this last that could not be ignored. It does not matter, except as an indicator of his poor grasp of political reality, that Mr Brown thinks he could have beaten Mr Blair in the contest for the Labour leadership, and hence the premiership. What matters is the persistent and public hawking of this belief. The Chancellor claims he did not discuss the leadership contest with Mr Routledge. This is not true. In an interview in the Treasury he uttered these words which, as his biographer noted, said it all: "The newspapers, with a few notable exceptions, did not back me - not least because I was out of fashion. I was never part of the London scene anyway. But that did not in my view mean much, once the campaign started among ordinary Labour Party members and indeed backbench MPs."

By publicly coveting his neighbour's job, and apparently regretting his decision to pull out of the contest four years ago, the Chancellor puts himself in the wrong. More than simply coveting the premiership, the book makes it clear that Mr Brown still blames Mr Blair's supporters for plotting against him to deny him his rightful reward. Again, it does not matter whether he is right. If Mr Brown thinks that his past resentment is more important than the task in hand, he is a smaller person than he thinks he is.

If the Chancellor really were the figure of stature which Mr Blair has always generously maintained he was, he would have said loudly and often: "Tony Blair is the Prime Minister I could not have been. We owe the scale of our election victory to him and I will do all I can, publicly and privately, to support him for as long as he wants me to."

The danger in this government was never going to be simply disagreement over policy. The truth is, you could barely persuade a cigarette paper to slide between Messrs Blair and Brown on the issues that really matter. When the Tory splits started, it was damaging not just because they disagreed, but because they had grown to dislike and distrust each other, and so could not resolve their dispute.

Both Mr Blair and Mr Brown would like us to believe that their relationship is still strong enough to resolve differences. Indeed, it would have been a lot better for Mr Blair if he had told his advisers to hold their fire this weekend. But the speed with which this crisis has blown up (and be in no doubt, it is a crisis) does not inspire confidence. Although Mr Blair's irritation should have been kept within his circle, and addressed only to Mr Brown himself, it is not up to the Prime Minister to end this row. Mr Brown needs to give ground, openly and graciously. Above all, he needs to realise that his tactics are counterproductive. Not only are they undermining his prospects of realising the Government's best hopes; his own leadership prospects are weakening by the day.