YESTERDAY, a Labour MP directed me towards a satirical website called the Brains Trust. The loyal Blairite was keen I should read a cutting titled, Prime Minister Released By FBI.

It went: "The Prime Minister was yesterday released from custody by the FBI, which had been holding him on suspicion of being a dangerous pacifist.

"The Prime Minister told us: 'I was flabbergasted when they picked me up. I mean, do I look like a pacifist? I'm trying to start a war for Christ's sake. It's obviously a case of mistaken identity'.

"It is understood the FBI had meant to arrest a socialist sympathiser called Tony Blair, known to have been a dedicated member of CND in the 1980s.

"Despite a nationwide search, nobody matching Mr Blair's description has been seen since the early 90s.

"The FBI have confirmed they realised they had made an error when 121 Labour MPs told them that Tony Blair was not the man they thought he was."

It is unkind. Cruel, even. But, as the MP pointed out, it sums up Tony Blair's predicament perfectly. He is questioned by the Yanks for his reluctance to start bombing Iraq. At the same time, damned by his own party for being a war-mongerer. Downing Street was a mixture of wounded and apoplectic at US Defence Secretary Donald Rumsfeld's "hypothetical" suggestion he may go to war without Britain. (Who can blame them. They spend the best part of a year trying to get somewhere, only to be told they weren't really needed in the first place.)

But more serious are the ructions back home. For the first time, Labour MPs are thinking the unthinkable. Life without Blair.

If he sanctions a bloody military campaign without the full backing of the international community there really is a slim chance he could go, they say. It is no longer about whether Mr Blair will stand down - at a time of his choosing - to make way for Gordon Brown. It is a fight for survival.

The MPs know Blair remains the party's most natural leader and will never forget how ruthlessly he ended the Tory monopoly on power - securing seats they were never expected to win in the first place.

But they found the sight of him - brow covered in sweat - being questioned by Trevor McDonald and a fractious studio audience very uncomfortable viewing.

One said to me: "What next? An appearance with Martin Bashir?" Another wondered whether Blair's touch for winning over public opinion had deserted him. Ministerial aides are threatening to resign - realising that giving up a job on the fringe of Government is better than being booted out of their seat altogether by an unforgiving electorate in 2005.

Left-wingers and union leaders have started dusting down the rule book on How To Challenge A Labour Leader.

The party's Campaign Group went so far as to issue a statement saying: "It is time for the Prime Minister to consider his position. We are now placing at risk the entire fabric of the international community. Blair is not the issue, the future of the UN is."

And even the stock market reacted, falling to its lowest level since the last time a Prime Minister was on the ropes - 1995's leadership challenge to John Major by John Redwood.

In a few months we may look back on this moment and recognise that life without Blair was always unthinkable.

If invasion is swift, Saddam is toppled and a stockpile of weapons of mass destruction is uncovered he may even emerge with his reputation enhanced.

But for now these are extraordinary times, and not just for the satirists.

Updated: 10:19 Friday, March 14, 2003