The Prime Minister is determined to fight on, but Gordon Brown may have other ideas

Is it possible that Mr Blair has raised the possibility that he might stand down before the election?

The fragile truce between Tony Blair and Gordon Brown has ended. Ostensibly, the cause of the breakdown is a new book by a former adviser to Mr Blair narrating lurid accounts of the stormy relationship. The book, though, is a symptom of wider tensions. After all, the shelves already creak with books on the same subject. Other accounts have not provoked the extraordinary statement issued by the Chancellor earlier this week.

The fragile truce between Tony Blair and Gordon Brown has ended. Ostensibly, the cause of the breakdown is a new book by a former adviser to Mr Blair narrating lurid accounts of the stormy relationship. The book, though, is a symptom of wider tensions. After all, the shelves already creak with books on the same subject. Other accounts have not provoked the extraordinary statement issued by the Chancellor earlier this week.

An entire conference could be kept busy for weeks analysing Mr Brown's short statement, with its reference to the "deliberate peddling of lies... orchestrated to put the Treasury in a bad light". The term "orchestrated" stands out, implying a group activity involving more than one person, certainly more than the author of a single book. But the last few words are the most astonishing and revelatory. Mr Brown insists the orchestration will "not be tolerated".

The implication of that phrase is explosive. Think about it for a moment. No other cabinet minister, indeed no previous Chancellor, would be in a position to tell Downing Street publicly that perceived misconduct in the prime ministerial court, or from former courtiers, would no longer be tolerated. In effect, Mr Brown is reminding Mr Blair of his indispensability. Somewhere deep within that phrase is both an assertion of his frustrated power and a warning that, if things carry on as they have, one of them will have to go.

The reaction to this statement, not least in the Blairite court, has been that it was over the top, a sign of Mr Brown's paranoia. This ignores the fact that Mr Brown has had a fair amount to be paranoid about in recent months. The Chancellor is wrong if he detects an orchestrated Blairite conspiracy to rubbish him.

To extend his metaphor, there is no conductor orchestrating an onslaught. But there has been a series of attacks on him from those close to Mr Blair that would test any truce. I am sure Jonathan Powell did not expect his comments to be published, but it was hardly sensitive of him to tell Boris Johnson, as they waited on their bikes at a set of traffic lights, that Mr Brown would never be Prime Minister.

Meanwhile, newspapers have reported Cherie insisting that her husband planned to go on and on, partly to keep Mr Brown out of Downing Street; run inaccurate stories about discussions between Mr Blair and Mr Brown over the euro; and asserted that the five year plans were Mr Blair's personal vision, with Mr Brown kept on the sidelines. This is in a period when, until recently, the two of them had been working fairly well together.

It is when personal dramas combine with policy differences that matters can get out of hand. In the view of senior figures in Downing Street, internal tensions over policy are exaggerated, not least by supporters of the Chancellor. They argue that at most there is disagreement over no more than 10 per cent of what Mr Blair seeks to do - the rest relates to ambition, resentment and positioning.

There is no doubt these elements play a part, but the current situation is more complicated than that. I sense genuine concern over the choice agenda so enthusiastically adopted by Mr Blair, not only over the substance, but the lack of rigour in thinking through the policies and the values that underpin them. So far Mr Brown has been loyal, hailing the need for "personalised services". Even so tensions over the direction of policy are nearing the surface once more.

The truce began last November, when Mr Prescott famously hosted a dinner, acting as a mediator for both men after they had fallen out in public. Friends of the duo describe that evening as "cathartic". Mr Prescott is uniquely trusted by both figures. Indeed if there was not a John Prescott there would be a need to invent one in the current stormy climate. I am told that when the three of them first sat awkwardly around Mr Prescott's table, Mr Brown complained about his chair, that it was uncomfortable and too low. Mr Prescott rushed off to get the Chancellor a more satisfactory seat. He asked Mr Blair if he also wanted a new chair, to which the Prime Minster replied, "No, it's alright, Gordon has always looked down on me." That characteristically self-deprecating and accurate joke lightened the tense proceedings.

Even in a lighter atmosphere, I do not believe that there was a formal deal struck over the succession. How could there have been? These are sophisticated political figures who know they are partly at the mercy of events beyond their control. Still, Mr Prescott's recent public comments are revealing. When he told an interviewer that the "plates were moving", he added that he had taken part in "conversations" and was therefore in a position to know. Shortly after that headline-making interview, he observed that Harold Wilson surprised everyone when he resigned suddenly in 1976.

I am certain Mr Prescott did not make these comments to destabilise Mr Blair. On both occasions he was devastated by the frenzy his words generated. But they are very precise comments, not slips of the tongue. Is it possible that Mr Blair has raised the possibility, or indeed that Mr Prescott has raised it with Mr Blair, that there might be circumstances in which he stands down before the election?

I pose the question at the start of a period that will be supremely challenging for the Prime Minister. I know most of Mr Blair's weeks are billed as "the toughest so far", but not often by this columnist. For example, I was certain that Mr Blair would emerge unscathed from the Hutton report. That inquiry was sparked by a series of naively inaccurate reports and statements from a supposedly impartial, publicly funded organisation. The Butler report on intelligence, published next month, is different. The key question was never whether the intelligence was sexed up, but why it was so badly wrong and whether Mr Blair was right to believe in its accuracy with such an apparent passion.

This is much more dangerous terrain for Mr Blair. Some of the inquiry's witnesses tell me they are impressed with the forensic nature of the questioning, the determination to find out what really happened. I doubt the final judgement will be lethal, but there will be much meat in this report for Mr Blair's critics, and the issue of trust will move centre-stage once more. Then there are the by-elections in Leicester and Birmingham. In the background, Iraq remains an unpredictable wildcard.

Nearly everyone who knows Mr Blair asserts his determination to fight the next election and their expectation that he will do so. He has performed robustly well in recent weeks, but the future of a leader is partly dependent on events and personalities beyond his control. I note that when Mr Brown declared that he would not tolerate the attacks on him, Downing Street leapt to attention, condemning the book and desperately attempting to get parts of it removed before publication.

When Mr Brown finds a situation intolerable, the situation can change pretty quickly. It is time for Mr Prescott to host another dinner.

s.richards@independent.co.uk