Purnell - the cloaked assassin strikes.

Late night rewrites for today's Herald

GORDON Brown was bunkered down inside Number 10 last night watching his cabinet imploding as James Purnell, the Work and Pensions Secretary, uncloaked himself as a political assassin and became the third Minister to quit the government in as many days.

After a hiatus following the departure of Hazel Blears Mr Purnell, a rising Minister with a Blairite mantle , struck a deadly blow at the moment the polls closed in the European elections, telling Mr Brown he had to go for the sake of the party and the country.

In a resignation letter that spelled out in a few words the private thoughts of several cabinet Ministers Mr Purnell told the Prime Minister: “ Your continued leadership makes a Conservative victory more, not less likely."

He added: "I am therefore calling on you to stand aside to give our party a fighting chance of winning."

Mr Purnell pointedly said he was acting alone and not putting himself forward as a candidate for Prime Minister. The focus then moved to his close friend David Miliband, the Foreign Secretary, who could rekindle his leadership ambitions and was tipped as the next resignation. Late last night Mr Miliband said he would not be resigning and described Mr Purnell's move as a mistake. John Hutton, the Defence Minister also backed Mr Brown, and Northern Ireland Secretary Sean Woodward, giving the Prime Minister hope that he might prevail.

Mr Brown, who was bracing himself against an unruly backbench revolt after a series of disastrous results in the English County Council elections and the European poll, was said to be in a "determined" mood as the chances of him surviving over the weekend diminished with each TV news bulletin. The coup, launched from inside the cabinet, was unprecedented in the Labour party and in recent political history.

Mr Brown, who was being backed by Peter Mandelson in Number Ten last night, could attempt a re-shuffle this morning. He is constrained by his need to attend the D-Day commemorations in Normandy on Saturday, giving the first regicide in Labour’s history an eerie echo of Margaret Thatcher’s political demise while she was in Paris.

Mr Brown’s fate overnight hung on three sets of numbers: the results from the County Council elections, the number of backbench signatures on an e-mail circulating among Labour MPs calling for him to go, and whether more cabinet ministers would break ranks and attack him.

At one stage yesterday a backbencher opposed to Mr Brown’s leadership accepted that he would resist an e-mail appeal unless the cabinet moved against him. Mr Purnell’s dramatic intervention gave the hotmailed petition more momentum. Shiobhain McDonagh MP, who called for Mr Brown to resign last year, said Mr Purnell's "bravery" would give Labour MPs the "courage and backbone" to sign up against the Prime Minister

Graham Allan MP came out immediately to back Purnell as replacement leader who would swiftly call a general election. Mr Purnell, 39 year old MP for Stalybridge and Hyde, was previously touted as leadership material and his reforms of long term unemployment benefits show his reforming, Blairite, credentials. His dramatic attack on the Prime Minister left him in poll position to take the crown if Mr Brown’s reign comes to an end, though he said he would not put his name forward.

Jack Straw indicated his backing for the Prime Minister late last night but it appeared that other Ministers were mulling their conscience and their e- mail in-boxes. The Conservatives quickly renewed their call for a general election to replace the "paralysed" government and the Lib Dems .

Caroline Flint, the Europe Minister, who had been seen as the next cabinet resignation. remained loyal to the Prime Minister, who was himself described as being in a “determined” mood. He showed at Prime Minister’s Questions that he is capable of fighting his way out of a tight corner and his raw political skill could see him through a rebellion only to leave Labour divided and at war with itself.

According to the script of the unfolding coup, she was due to time her departure with the closing of the European and local government polls at 10pm last night. However she instead issued a pledge of loyalty. Ms Flint’s departure on its own would not be enough to sink the Prime Minister but Mr Purnell's coup de theatre was in a different league.

There were no indications during the day yesterday that senior cabinet Ministers, in particular Health Secretary Alan Johnson, had the appetite to take on Mr Brown but this morning the game had changed entirely.