Prime Minister Tony Blair will today cave in to demands from rebel Labour MPs to set a timetable for his departure - announcing that he will quit within a year.
Mr Blair will make his announcement following the shock resignation of junior defence minister Tom Watson and a string of junior members of the government who quit their posts as Parliamentary Private Secretaries.
Sources within No 10 let it be known that Mr Blair would use a pre-planned photo opportunity with Education Secretary Alan Johnson to make his intentions plain after a day of turmoil at Westminster.
Mr Blair's dramatic move will come despite the fact that he has always insisted he would serve a full term as premier, having seen Labour elected back into power only on May 5 last year.
Senior sources within No 10 confirmed last night that Mr Blair felt he now had to give clarity to his party and the country about his intentions.
But none were prepared to go on the record confirming the Prime Minister's intentions after a day of high drama.
The revelation about the timetable followed one of the most serious political crises of Mr Blair's premiership.
Mr Watson and seven Parliamentary Private Secretaries resigned from office over the course of yesterday.
The last of them to go, after 9pm last night, was Hartlepool MP Iain Wright, PPS in the Department of Health.
Mr Wright, elected to succeed Peter Mandelson at a by-election in 2004 and a PPS for just 10 weeks, said he "believed that the party and the Government cannot renew itself in office without urgently renewing the leadership".
He also blasted a review of maternity and paediatric services in Teesside - a move which could have serious consequences for the future of Hartlepool hospital. The hospital's future was a key issue in Mr Wright's by-election victory two years ago.
The earlier apparently coordinated move brought a furious reaction from Mr Blair, who earlier accused Mr Watson of being "disloyal, discourteous and wrong" in signing up to a round-robin letter from 15 MPs calling on the premier to stand down.
And in a letter to Mr Watson, Mr Blair sent out his message that attempts to get him to step down or name his departure date were harming the party and were "divisive ... and totally unnecessary".
Later Health Secretary Patricia Hewitt said the MPs who had signed the letter had committed an act of "immense disloyalty and foolishness".
Ms Hewitt said the group was trying to engineer a "coup" to replace Mr Blair.
She said: "Well all I know is that 15 people signed - a rather small proportion let me say of the Parliamentary Labour party - they signed that letter for themselves.
"It looks as if they are trying to engineer a coup. That as I say is an act of immense disloyalty and foolishness."
Party chair Hazel Blears warned: "We must not allow these next few months to be marred by rancour and division. We remember those bad old days when we spent so long arguing amongst ourselves, we forgot to fight the Tories. When Labour is divided, only the Tories benefit."
Speaking from India, Conservative leader David Cameron said the Government was in "meltdown" and Mr Blair was a "lame duck".
Later, Environment Secretary and South Shields MP David Miliband called for an "energising, refreshing transition" of the Labour leadership to Gordon Brown when Mr Blair leaves office.
He said Mr Brown would be "a very good leader" and appeared to rule himself out of running for the position of leader or deputy leader of the party.