She added: "My concern would be that I have a very tough contest in my constituency and I need to devote the maximum amount of time to that contest, to represent my constituents.

"However, Labour needs to win the election for Liverpool's sake – and, to do that, we have to be a credible force."

The odds are on Mr Brown leading Labour into the election, probably in May, primarily because ministers calculate that removing him so close to the poll would harm the party.

Nevertheless, many Labour MPs have arrived back at Westminster seething over the latest expenses' embarrassments, and blaming the Prime Minister for the Legg inquiry that revealed them.

They are also dismayed at Mr Brown's failure to close the huge opinion poll gaps with the Conservatives, which points to likely defeat.

In that atmosphere, the election of an "anti-Brown" candidate to lead the PLP would deal a blow to the prime minister's authority, fuelling claims

that he is losing control of his party.

Since resigning, Ms Kennedy has criticised Mr Brown's leadership style, comparing him with a "Mafia boss" who "might not pull the trigger, but he knows who's getting bumped off".