Doubt surrounded the future of the Chancellor tonight after Gordon Brown said Alistair Darling had made a "mistake" over his expenses.
The Prime Minister was forced to fend off a flurry of questions over the chancellor's position after Mr Darling admitted he would be paying back hundreds of pounds and apologised "unreservedly".
The Lib Dems demanded Mr Darling go because he no longer had the "moral authority" to manage the nation's finances.
Meanwhile, the Tories accused Mr Brown of "hanging him out to dry" by refusing to say whether he would stay in his job.
For his part, the chancellor insisted it was "the PM's call" whether he should be removed in a reshuffle expected after local and European elections on Thursday.
A poll tonight provided more evidence that Labour faces a major backlash from voters. Research by Ipsos Mori found the party's support has slumped 10 per cent over the past month, and it is now running neck and neck with the Lib Dems on 18 per cent.
Some 40 per cent said they would be voting for David Cameron's Conservatives at the next general election.
Mr Darling returned to the heart of the expenses row this morning, when the Daily Telegraph reported that, in July 2007, he submitted a £1,004 claim for service charges on his south London flat up to December of that year.
Soon afterwards he became chancellor, moved into Downing Street and began renting out the flat.
In a round of broadcast interviews this evening, Mr Darling said he had made a "mistake" and would repay £350.
"I'm sorry about that, I unreservedly apologise," he said.
However, he denied claiming on two properties simultaneously, and insisted he did not want to be seen to have made "any gain" from the situation.
Asked whether he was expecting to be removed from Number 11 in a reshuffle, Mr Darling replied: "It is up to the Prime Minister. He has got to decide the team that he wants to be in the next government.
"Gordon and I work very, very closely together, but at the end of the day it is his call."
He went on: "When the Prime Minister has his reshuffle, it is the Prime Minister's call."