The Week in Politics: Westminster finds itself wondering about life after Blair

The phrase has suddenly entered the language at Westminster: "The post-Blair era". Tony Blair's crisis over Iraq is so deep that Labour MPs, even those loyal to him, cannot help but discuss what will happen if he is forced out of office. Cabinet ministers join in and are quietly forming new alliances. Not that they want Mr Blair to fall, you understand, but just in case.

Politics is always a rough trade. Its normal rules have been suspended by Iraq. As well as the behind-the-scenes plotting over the succession, there have been some extraordinary events in the past week. I cannot imagine that a cabinet minister has ever survived in post after launching such a stinging attack on a Prime Minister as Clare Short did last Sunday. Yet she was still at the cabinet table on Thursday, outlining plans for humanitarian relief in Iraq as if nothing had changed.

On the same day, the Tory leader, Iain Duncan Smith, emerged from No 10 and, without warning Mr Blair, did a bit of moonlighting as his official spokesman by announcing that winning a new United Nations resolution was "further away than it has ever been". Jack Straw, the Foreign Secretary, had to give an unscheduled "doorstep" interview so that the Government voice was heard.

There were no complaints from Mr Blair about Mr Duncan Smith's briefing. Another oddity of the current scene is that, despite the Tory leader's weak position in his own party, Mr Blair needs the Opposition's support in a critical Commons vote on Iraq expected next week. The inevitable Labour rebellion makes the Tories' three-line whip vitally important for Mr Blair. Strange times indeed.

It has been a gloomy week inside Downing Street. The tension was illustrated by some Blairites' instinctive feeling that Gordon Brown was behind Ms Short's outburst. "You have to ask who benefits from this – it's Gordon," one Blair aide said. The theory is that the Chancellor fears he may miss the boat unless he takes over soon, since the shine is coming off his reputation on the economy.

There is no evidence to support the idea that he colluded with Ms Short. But the Blair circle has been wary of her since receiving intelligence from inside her department that she fancies the dual role of Deputy Prime Minister and Foreign Secretary if Mr Brown succeeds Mr Blair.

In an attempt to quell the Labour rebellion, Mr Brown was fielded for television and radio interviews on Thursday. As he doesn't often talk on foreign affairs, they provided a fascinating glimpse of what Prime Minister Brown would look like – pretty impressive.

Some Blairites noted that, as usual, Mr Brown did not refer to Mr Blair as Prime Minister or "Tony" but as "Tony Blair" – as if he could not accept that Mr Blair has the top job or did not want to be too informal.

But Mr Brown said something very significant on BBC2's Newsnight programme. "I think people will want to continue to support Tony Blair's leadership ... He should be given 100 per cent support in his efforts, not only over the next few days but over the next few years."

By referring to a "few years", Mr Brown sent a message to Mr Blair that he is not after his job. No doubt he was trying to cool the feverish talk from some of those around the Prime Minister, who distrust Mr Brown's every move. Mr Brown feels he cannot win; he cannot decide Mr Blair's fate and, like the Prime Minister, must wait on events.

The Chancellor would certainly be the most likely beneficiary of Mr Blair's downfall. He is the front-runner to succeed him by a mile. Alan Milburn, the Health Secretary, would be fast out of the starting blocks. Indeed, Brownites claim he has been running for several months, using his plans to set up foundation hospitals as an excuse to portray the Chancellor as an Old Labour opponent of public- sector reform. One cabinet minister told me: "Milburn is putting out feelers to see who is on board. It's not Blair versus Brown. The two camps now are Brown and post-Blair."

Who else would run? David Blunkett believes Britain is not ready for a blind Prime Minister. Jack Straw is too locked in to Mr Blair's strategy on Iraq. It it too soon for David Miliband, who some believe was marked out as a possible successor by Mr Blair when he promoted him so quickly to Schools Standards minister.

But Robin Cook, who is expected to resign from the Cabinet if there is a war without UN backing, might find taking on his auld enemy Mr Brown irresistible. Their personal feud dates back 20 years.

Other possible runners include Charles Clarke, the Education Secretary, and Peter Hain, the Welsh Secretary, though they are allies and would not stand against each other.

Will it happen? Mr Blair has never been loved by his own party. It has tolerated him because he is such an electoral asset. But Mr Blair has always known he could suffer a haemorrhage of support if he ever began to struggle.

Forget the self-defeating talk on the Labour left of a formal challenge to his leadership. As Margaret Thatcher found, it is not about the party rule book but whether the leader loses the confidence of his or her party.

Anything could happen. But my hunch, for what it's worth, is that Mr Blair will somehow find a way through. Yesterday, the Downing Street gloom lifted very slightly: the Labour rebellion may be eased by President Bush's Middle East "road map" and the Government's campaign to blame France for the UN deadlock. The post-Blair era may be some way off yet.

a.grice@independent.co.uk