TONY BLAIR was under mounting pressure to rein in his supporters last night amid fears that their provocative behaviour over the past 48 hours could drag the Labour Party into full-scale civil war.

Allies of the Prime Minister and the Chancellor traded blows in writing over the weekend, with the ultra-Blairite Stephen Byers and Alan Milburn demanding that Gordon Brown should lay out his plans for government straight away.

Mr Milburn further heightened tensions by insisting that no single figure in the Labour Party had a “monopoly on wisdom” — a move widely interpreted as a personal attack on Gordon Brown.

Writing in The Sunday Times, he said: “Replacing Tony Blair will not in itself renew Labour. Renewal means more than changing the guard.”

But suggestions that the Chancellor should “put up or shut up” were greeted angrily at the Treasury. Ed Balls, the Economic Secretary to the Treasury and one of the Chancellor’s closest allies, dismissed suggestions of a prolonged debate. “I do not believe the Conservative Party can win the next election. But we must make sure we do not lose it. The idea that we need a period . . . of internal navel-gazing in which to renew is absurd,” he wrote in The Observer.

Allies of the Chancellor believe that the Blairites want to prolong the “debate” long enough for an alternative successor to Mr Brown to be groomed.

Many MPs reacted with dismay at the renewed tensions, sparked off by Mr Blair’s interview with The Times on Thursday, in which he refused to lay down a departure timetable and insisted that he would not do so before or during the party conference.

A BBC survey of 68 Labour MPs conducted after the interview revealed that 40 believed that he should go within the next year.

Furthermore, 39 of those polled said that they believed it would be helpful for him to lay out a timetable during or before the party conference.

But over the weekend the arguments over whether the Labour Party should have a “debate” changed into a proxy for the leadership battle among allies of the Prime Minister and the Chancellor.

One Labour source said: “If we’re now in a situation if people who say ‘we’re for a debate’ are accused of being anti-Gordon, then that’s ridiculous. After all it was Gordon who called for a big debate a year ago.”

But senior Labour figures made clear their irritation at the behaviour of the “ultras”. Jack Straw and Peter Hain — both of whom have ambitions to take over from John Prescott as deputy Labour leader — were the first to launch a counterstrike. Mr Straw said: “It is profoundly important for the party’s future that we don’t invent ideological or policy divisions where, in truth, they don’t exist.”

Mr Hain claimed that politicians on the “marginalised fringes of the party” were putting Labour’s prospects of re-election at risk.

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