These are the MPs who have so far stated publicly which camp they support:

FOR A BALLOT:

GEOFF HOON - Former chief whip and Cabinet minister and co-signatory of the letter calling for a vote.

PATRICIA HEWITT - The letter’s other signatory, and a former health secretary.

CHARLES CLARKE - A long-time critic of Mr Brown’s leadership, the former home secretary has promised to back the PM if he faces a ballot and wins.

FRANK FIELD - The leader of the 10p tax rebellion against Mr Brown and a former welfare minister.

BARRY SHEERMAN - Senior backbencher who has already called publicly for the PM to be removed.

AGAINST A BALLOT:

ED BALLS - Mr Brown’s closest Cabinet lieutenant said the Government had “more important things to do than get distracted by a small minority of MPs” who do not speak for Labour.

ANDY BURNHAM - The Health Secretary - widely seen as a leading Blairite - made clear through a spokesman that he continues to back Mr Brown.

SHAUN WOODWARD - The Northern Ireland Secretary was the first Cabinet minister to speak publicly against a secret ballot, which he condemned as “a huge distraction that nobody wants”.

LORD MANDELSON - A spokesman for the Business Secretary said that the PM “continues to have the support of his colleagues and we should carry on Government business as usual”.

TONY LLOYD - The chairman of the Parliamentary Labour Party, who insists a vote is not wanted by the vast majority of Labour MPs.

JOHN MCDONNELL - Prominent left-winger who tried to challenge Mr Brown for the leadership, who said rank-and-file Labour members would be “aghast at the renewed factional infighting”.

JOHN MCFALL - Chairman of the Commons Treasury Committee, who described the ballot call as “a death wish”.

CHRIS BRYANT - Europe minister, who described the Hoon/Hewitt initiative as a “damp squib”.

SADIQ KHAN - Transport minister who insisted Mr Brown was “the only person” for the job of PM.

DAVID BLUNKETT - Former Cabinet minister who said a ballot was “not wanted... and not needed”.

MARGARET BECKETT - Former foreign secretary said Labour would be “completely mad” to think about removing Mr Brown as leader.

GERALDINE SMITH - Loyalist backbencher who dismissed Mr Brown’s internal party critics as “joke figures” and said there was no appetite for a vote among MPs.

JOHN MANN - Labour backbencher who dismissed Mr Hoon’s involvement as “sour grapes”.