FOREIGN Secretary David Miliband is being warned by allies that he will have "missed his chance" if he fails to mount a leadership challenge to Gordon Brown this summer.
Miliband is being pressed by backbench supporters to 'throw his hat into the ring' in order to force the Prime Minister to quit within the next few months.
But they are also piling pressure on Miliband, telling him that he will not be supported if
– after an election defeat in 2010 – he decides to go for the leadership then.
The warning came as Labour rebels refused to back down in their opposition to plans to allow terror suspects to be detained without trial for up to 42 days.
One senior Labour source said: "David Miliband won't get the leadership if he goes for it when it's easy, after Brown has lost the election. He is being told he should go for it now, or he won't be backed later."
Former Labour deputy prime minister John Prescott fuelled speculation in a speech in Wales by referring to Miliband as a "leader", while cautioning the party not to mount a challenge against Brown. He said of Miliband: "He is quite a brilliant man and he will be one of our leaders."
The pressure on Miliband comes amid intense speculation that he could succeed Brown, following the disastrous Crewe and Nantwich by-election two weeks ago when the Conservatives turned a 7,000 Labour majority into an 8,000 majority for themselves.
Downing Street attempted to draw a line under the speculation last week, as the Prime Minister sought to shift attention to his plans to ease the global oil crisis.
But Labour MPs and ministers are still known to be tormented about the party's election prospects. Allies of Miliband believe that if the Foreign Secretary took over ahead of the election, he would either lessen the losses they face under Brown, or even mastermind a revival which would see Labour returned for a record fourth time in succession.
The pressure on Miliband is all the more intense as he resisted calls from his allies to stand this time last year when Tony Blair announced his departure.
Labour rebels have warned ministers to back down over plans to extend detention without charge to 42 days for terror suspects. Brown and the Cabinet will meet MPs for a crunch meeting in Westminster tomorrow in an effort to face down about 50 Labour rebels opposed to the change. If all the rebels vote against the Government then the 42-day plan will fail.
Brown is expected to try to quell doubts about his faltering leadership in the wake of dismal results at the ballot box, a series of policy U-turns and rebellions over car tax.
Home Secretary Jacqui Smith will outline a series of concessions over terror laws at the meeting to try to stave off a potentially fatal defeat.
One of the rebels, Stockton North MP Frank Cook, said: "They are going to have to make quite a lot of concessions if they expect us to back down. Those of us who are of the same mind as I am on this are the ones who have thought about this at length and I think we are the less career-orientated.
"This is an important principle and it is absolutely non-negotiable for us. I don't understand why they are trying to press on with this. Their logic is fallacious. Their plans don't make sense."
In addition to attempts to woo rebels with concessions, Labour is also understood to be trying to secure the votes of Unionist politicians from Northern Ireland. One possible incentive might see some of the nine DUP members offered seats on the intelligence and security select committee.
Brown's predecessor Tony Blair suffered his first Commons defeat when he tried to extend the limit for detention without charge to 90 days in 2005.
