By Nick Assinder
Political correspondent, BBC News website
So much for a period of calm and an end to Labour's in-fighting.
How long will Gordon Brown's smile last?
Former Home Secretary Charles Clarke has lobbed a hand grenade into the fragile peace with a brutal, personal attack on Chancellor Gordon Brown.
He echoed the views of many of the prime minister's allies when he suggested Mr Brown is currently not fit to be prime minister and that "Ultra" Blairite Alan Milburn has the right stuff to replace Mr Blair.
Indeed, his references to Mr Brown's "stupid" behaviour, nervousness and lack of confidence recall the infamous claim some years ago, and said to have come straight from Downing Street, that the chancellor suffered from "psychological flaws".
His intervention seems designed to ensure that there is a senior, cabinet level, Blairite challenge to Mr Brown whenever the leadership election comes.
And the mention of former minister Alan Milburn - once seen as a probable contender but whose star rapidly waned after his much-criticised handling of the last general election campaign - seems designed to infuriate the Brown camp.
But Mr Clarke's interview has also ensured that the bitter wrangling which marked the past week will now continue unabated for the foreseeable future
Mr Clarke has reignited Labour's civil war
While the past few days could be characterised as the campaign to "get Blair" the next phase looks like being "get Brown".
And, while Tony Blair and his friends may be happy to see the chancellor's prime ministerial credentials put under the microscope - in the belief they will be found lacking - they will be less delighted that the civil war is back on.
Mr Brown may bite his tongue, but his allies will not. And within moments of Mr Clarke's interview emerging, there were some furious rumblings from within the chancellor's camp.
There will be the inevitable suspicions that Mr Clarke was acting with Mr Blair's blessing, just as it was claimed Mr Brown was behind the attacks on Tony Blair.
Neither claim is likely to be right, it is probably more a case of allies - and, in Mr Clarke's case an independent-minded individual - speaking their minds and not being pulled back by their men.
Mr Clarke was, after all, sacked by Tony Blair over the home office shambles and has also previously launched attacks on the prime minister.
Only a few days ago he delivered a weighty speech criticising both men and setting out his own thoughts on the development of Labour policy.
It was a thoughtful intervention designed to further the debate that has been encouraged by all sides over the party's future and was inevitably seen in some circles as his own tentative toe dipping into the leadership waters.
War goes on
Mr Clarke has denied leadership ambitions, but is clearly out to play a major role from the backbenches, at least.
The fact that Mr Clarke is one of the most senior and respected figures in the Labour party, who went through the mill with Neil Kinnock in the party's dark days, adds real power to his remarks.
So, the war goes on.
And that has ensured the issue of whether Mr Blair can really hang on for a year with this sort of stuff exploding around his head is once again the key question.
The carefully worded peace signals delivered by both Mr Brown and Mr Blair only 24 hours ago were not the result of some sort of deal between them, rather a mutual desire to stop the feuding that was damaging the whole government and the Labour party.
And it was always possible that the wrangling would continue anyway, despite all the calls from ministers and others for the rival camps to shut up.
The prime minister will attend the annual TUC conference next week, where all eyes will be on his reception, swiftly followed two weeks' later by the pivotal Labour conference.
The pressure on Mr Blair to now announce he will be standing down much sooner than next spring - possibly before the end of the year - will only intensify.
And any optimism from the Blair camp that their man had done enough to calm this storm and halt those demands for his resignation has been comprehensively dashed.