John Rentoul: 'The PM's authority is leaking,' they cry, and certainly the floor is getting slippery

For Brown and the whole Labour Party, these are treacherous times

Alastair Campbell calls it a media frenzy. Because he used to be Blair's press secretary, sophisticated members of the liberal media laugh it off and say he would say that, wouldn't he? Yes, he would. But that does not make it untrue. So much of the editorialising that passes for reporting over the past fortnight has been a lazy sigh of longing for the different, better, greener grass on the other side of the fence. The cliché of authority diminished as a substitute for thought or, for that matter, facts.

It is cookbook journalism. Into the mélange goes John Prescott, because he was a bit grumpy about the schools White Paper. Stir in the public dispute over the smoking ban. A pinch of David Blunkett protesting to Tony Blair against being made to kick the crutches away from disabled people. Then the two main ingredients. A large dollop of Blunkett's resignation. And, of course, a Labour rebellion cutting Blair's majority of 66 to - delicious - one vote. Well, it was actually two, because a whip miscounted, but then there were at least one and a half antis missing without a very good excuse, George "Hammer of Blair" Galloway among them.

The self-fulfilling maw of authority-drainage works by agglomeration. A number of unrelated matters has turned out less than optimally for the Prime Minister in the space of a few days. So it must be a crisis. Serve with a selection of clichés. Days numbered. Cabinet splits. Date of departure brought forward. Early transition. Grass greener with Gordon.

Meanwhile, in a parallel universe, a Labour government recently re-elected with a substantial majority is carrying out its manifesto promises, while also trying to protect people from terrorism after the 7 July killings by home-grown suicide bombers. In this universe, people are not interested in the Prime Minister's authority but in whether he is doing the right things for the country. On this, opinions on the unrelated issues vary. A reasonable person in this universe might, for example, hold the following views. Schools White Paper: not far enough. Smoking ban: too far. Sick pay: people who can work shouldn't be on benefit. Blunkett: right to go; should never have been brought back. Outlawing the glorification of terrorism: counter-productive and unnecessary.

In this universe, there is an intelligent debate being conducted in Parliament and the media about proposal to detain suspected terrorists for up to 90 days. On the BBC, journalists interview Lord Carlile instead of each other and identify the two central issues. There is the length of detention without trial, and there is the way in which detentions are supervised by judges. Lord Carlile, the independent reviewer of anti-terrorist laws, supports the principle of a 90-day maximum but wants a "more searching system" of judicial checks to make sure it is not abused.

Back on planet Earth, however, jaw-jutting prime ministerial aggression combines with the wilful refusal of journalists and Labour MPs to think beyond liberal-left slogans to produce a dialogue of the definite. Blair's argument for the 90-day power is that the police say they need it. For many journalists and Labour MPs, this is precisely why the police must not have it. It has come to something when Lord Carlile, a former Liberal Democrat MP, makes a better case for such legislation than a prime minister once admired for being able to persuade almost any audience of almost anything. With his access to the police and intelligence services, Lord Carlile says he is "aware of several operations" in which the inability to detain suspects for longer than the present 14 days has "made the difference between someone being charged or not". In a sane world, the Home Secretary could produce a compromise by which a special judge would be given powers to make sure that the police have sound reasons for keeping someone locked up. That would be better than the weak requirement currently in the Bill for the police to report every week to a district judge.

But we are not in a sane world. We are in a world where people resort to pre-cooked notions of arbitrary detention without trial, and where the Prime Minister challenges his own MPs to vote him down, "settle for an option that isn't the best option" and take responsibility for it the next time that terrorists strike.

This is, then, a treacherous week, not just for Blair, but for Gordon Brown and the rest of the Labour Party. The vote on the Terrorism Bill on Wednesday is a defining moment. There have, of course, been plenty of those, and plenty of "worst weeks". But as Blair tries to hand over the priceless Ming vase of stable and orderly government to Brown, all that leaking authority makes the floor slippery.

It may be that the worst thing that happened to Labour last week was not the media frenzy over Blair's authority, but David Cameron's weak performance on BBC's Question Time. Before it, a Blair ally, gloomy about the lemming tendency among his fellow MPs, told me that there was one consolation. "Cameron will smoke them out," he said. His arrival at the head of an invigorated Tory party would make them realise that they had to fight with discipline to hold the centre ground. But markets in political stock overshoot, like those in the City, and the Cameron bubble puffed him up beyond his equilibrium level. He is good, but not as good as we thought.

Certainly Gordon Brown must have watched Question Time with a growing sense of anticipation. If Labour can hold its nerve, Brown can beat Cameron. But that realisation may allow Labour MPs to indulge themselves. The question is how to get from here to a Brown victory without dropping the Ming vase. Blair will keep his balance. So, I think, will Brown. But they could so easily be tripped up by the rest of their party.