Leading article: The political storm clouds are gathering over Mr Blair

The Deputy Prime Minister admitted yesterday that he had "behaved stupidly" in conducting an affair with his political diary secretary, Tracey Temple. Were there not other strong candidates for the accolade - how about the Home Secretary's disclosure that "very few" (meaning 288) of the missing foreign prisoners had been released after he was alerted to the problem? - John Prescott's admission might have stood a good chance of being recognised as the understatement of the year.

Stupid is the very least of it. Never among the heaviest political hitters in the Government, Mr Prescott nonetheless had his place. His presence allowed Tony Blair to claim that he had not betrayed the working-class roots of the Labour Party. He was a reputed honest broker, in touch with the party rank and file. It would be up to him, it was said, to inform the Prime Minister when it was time to quit - and, it was confidently predicted, Mr Blair would have no choice but to listen.

Now, even that measure of authority has gone. It is not only the lurid, if puerile, claims of Ms Temple that have destroyed it, but Mr Prescott's belligerent response. Yes, he did have a relationship, but Ms Temple had published her diaries to "maximise financial gain". This is not a good start to a dignified defence of the indefensible. The odds on John Prescott holding on to his job are now judged so poor that some bookmakers have suspended betting on how long he might last in office.

That there has not so far been greater pressure on Mr Prescott to resign reflects several considerations. He was regarded as a bit of a buffoon, even before the revelations: there were few illusions to be shattered. More importantly, there was a widespread understanding that, despite the title of Deputy Prime Minister, he was rather far down the government pecking order in terms of authority and responsibilities. For the time being, the case for Mr Prescott's resignation remains personal: if he leaves office, it should be for his own sake and that of his family. If, however, it turns out that he has abused the privileges of office in pursuit of his affair, his position would be untenable. Ditto if allegations now emerging about his lecherous behaviour are true: this would raise questions of unacceptable sexual harassment.

Although the loss of the Deputy Prime Minister would undoubtedly undermine Mr Blair's authority further within the parliamentary party, it is far from being the main danger to the Prime Minister and his government in the coming week. This lies in the Home Office, where officials are spending the holiday trying to track down the thousand or more foreign prisoners who should have been considered for deportation.

The more that comes out about this débâcle, the more apparent it is not only that successive Home Secretaries neglected the issue, but that such facts as have emerged have so far been presented in the best possible light. The most serious offenders may have been found on the police computer, but this does not mean their actual whereabouts is known. The call for Mr Clarke's resignation by a woman who claims she was raped by one of these offenders shows that there is at least one serious new charge going through the system. The likelihood must be that there is worse, perhaps far worse, to emerge, probably before Thursday's local elections.

A circumspect Mr Blair catered for this eventuality with his unusually equivocal support for Mr Clarke in yesterday's News of the World. It is illogical, but true, that a proven murder or rape by one of the 288 foreign prisoners released on his Home Secretary's watch could force Mr Clarke from office. And the loss of so stalwart a political ally would not only upset the balance of the Cabinet, but inevitably weaken the Prime Minister.