GORDON BROWN faced an inevitable challenge to his expected succession to the Labour leadership as the Left, led by Clare Short, united in outrage last night at his support for a new nuclear deterrent.

The Chancellor, who will also back a parliamentary vote on an issue on which the Government is certain to win, was given a severe warning by several of his long-standing allies that they could no longer vote for him when Tony Blair stands down. They accused the Chancellor of being desperate to secure backing of the Blairites.

The most prominent critic was Ms Short, who was close to Mr Brown throughout her years in the Cabinet and has often backed him to replace Mr Blair. Now Mr Brown will not be given a clear run and John McDonnell, chairman of the far-left Campaign group, is being touted as a possible rival.

Within Whitehall Mr Brown was being criticised for the strange manner of his declaration — using his annual economic address at the Mansion House to indicate that he would be ready to back a replacement of Trident if that is what the military chiefs want.

Downing Street, which had received little advance warning of Mr Brown’s announcement, and the Conservatives tried to pretend that nothing had changed. But that was not the true view in Government or the Labour party, where it was accepted that Mr Brown had given a deliberate pledge to renew Trident from which he would be unable to retreat.

By saying that he would back the system in the long term he was going beyond the manifesto pledge to maintain it through the Parliament. Backing in the long term means replacement.

Ms Short was clear about what Mr Brown had done and said that she would no longer support him as Labour leader. “It’s not just a question of whether Britain has a nuclear weapon,” she told the BBC Radio 4 The World at One programme. “It’s about the whole of the UK’s place in the world and how we correct the mess we are in in the Middle East and what we do about nuclear proliferation and how we shift the world to a multilateralism that’ s focused on dealing with global warming and the rising world population and all these enormous threats we face.

“And to just, in a Mansion House speech that’s meant to be about the economy, throw it away and say, ‘This is what we are going to do’ — I can’t support that kind of leader, absolutely not.” She added: “It means a lot people who were happy to see Brown take over as leader will now think there’s got to be a contest and we’re not willing to support him.

“I think it’s part of his desperation, that is sort of so humiliating him, to prove to the Blairites that he’s as right-wing as Blair and that therefore they will keep their promise to hand over to him.”

Lord Gilbert, a former Defence Minister, backed the retention of a deterrent. “I’m delighted. He’s foreclosed the debate, I hope, very largely."

Liam Fox, the Shadow Defence Secretary, called for a vote on Trident in the Commons and said that the Tories would ensure this happened.

Jeremy Corbyn, a member of the Socialist Campaign Group of left-leaning Labour MPs and the national vice-chairman of CND, said: “Gordon’s announcement of spending up to £25 billion on Trident replacement is sad and wrong. A Trident replacement would be illegal, and removes any arguments we might have for opposing the proliferation of nuclear weapons in other countries.”

The protests against Mr Brown’s announcement were stepped up through the day. The annual conference of Unison, the country’s largest union, voted to oppose the replacement of Trident.

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