McDonnell set to challenge Brown

Former environment minister Michael Meacher stood aside to allow Mr McDonnell to stand on a "united left platform" after the two men agreed to pool their support in the hope of securing the 45 MPs' nominations needed to get on to the ballot paper.

Mr Meacher's withdrawal came as nominations opened for the leadership and deputy leadership, with would-be deputies Harriet Harman, Peter Hain and Hazel Blears swiftly announcing they have the necessary support to join the contest to replace John Prescott.

Mr Brown's leadership campaign continued in full swing, with a visit to Southampton to highlight his plans to build social housing and eco-friendly homes.

Mr McDonnell, calling on MPs to nominate him to ensure an election for the leadership is held, insisted a contest in a spirit of "friendly comradeship" would leave Labour "stronger and more united" to take on the Conservatives at the next General Election.

He urged the Chancellor to make good on his claim that he would welcome a contest by creating a climate within the party where MPs feel able to nominate him as a challenger.

Speaking at a hastily-arranged press conference in a cramped Westminster meeting room, Mr McDonnell said: "What we are doing ... is launching an appeal to Labour MPs to nominate the only candidate that there is to ensure that there is an election for the leader of the Labour Party. We are doing that not just because we want them to support our political platform, but also because if they don't nominate, hundreds of thousands of party members and trade unionists will be denied the opportunity to vote for the leader of this party. This is an issue of democracy."

Mr Meacher said he agreed to stand aside in favour of the chair of the Socialist Campaign Group after they compared lists of supporters and found Mr McDonnell had more. Neither would reveal how many names were on their lists, though they did confirm that some had to be removed because they offered their support to both men.

Mr McDonnell said he is "confident" they have enough expressions of support between them to secure a place on the ballot paper, but he stressed that these pledges must be converted into formal nominations by Thursday's deadline.

The McDonnell campaign is expected to focus on reducing wealth inequality, building affordable houses, tackling climate change, fighting pensioner poverty and establishing a more independent foreign policy.