A Labour backbencher has apologised for submitting an expenses claim for a £5 donation he made at a church service commemorating the Battle of Britain.
Frank Cook made the offering in his Stockton North constituency in 2006 and submitted the claim with a handwritten note, the Sunday Telegraph reports.
Mr Cook said he did not recall the claim - rejected by the Commons Fees Office - and that it was "a mistake".
It comes as party leaders make more calls to reform the MP expenses system.
The government is considering introducing a legally-binding code of conduct for MPs that would cover minimum standards of service to constituents.
Tory leader David Cameron has given his backing to Liberal Democrat calls for powers to allow voters to force out MPs who break Commons rules.
Lib Dem leader Nick Clegg has suggested a "recall" mechanism that would be triggered if 5% of constituents signed a petition demanding a by-election.
It would only apply to someone found guilty of wrongdoing.
'No other claims'
Meanwhile, Mr Clegg has said the chancellor, Alistair Darling, should resign over claims in the Daily Telegraph he switched the designation of his second home four times in as many years.
Mr Clegg told the BBC it was impossible for Mr Darling to continue in his job when such major question marks were being raised about his financial affairs.
Mr Darling has said his claims were within the rules of the Commons, which are designed to reflect the fact that MPs have to meet the cost of living in two places.
In its latest expenses story, the Sunday Telegraph says the handwritten note attached to Mr Cook's donation claim read: "Battle of Britain church service, Sunday 17.09.06. £5 contribution to offertory on behalf of Frank Cook MP."
Mr Cook expressed shock at the discovery by The Sunday Telegraph of the note.
He told the BBC that he took full responsibility for the claim he could not recall putting in the claim and had no record of it.
"It's been my error. An inexcusable error. An error for which I am full of regret.
"Why on earth I did it, I don't know. I can't have been thinking at the time.
"I must have been just rushing through the paperwork, and I've got to say that I regret doing it. It should never have been done. It's unjustifiable and I'm very sorry. And I'm so pleased that the Fees office spotted it as they did"
He said he would now be going over his other expenses claims to check for any mistakes.
Personally I don't care what system we have so long as it is clear, open and credible with the public - and we have to get it done quickly
David Miliband Foreign Secretary
The Telegraph also reports on further claims made by other MPs, including reimbursement for bathmats and carpets bought in India.
David Cameron has also been explaining his second home claim.
The Mail on Sunday reports he paid off the remaining £75,000 of a mortgage on his London home using his own money, shortly after taking out a £350,000 mortgage on his constituency home in 2001.
He used the second homes allowance to pay the interest on the new mortgage. Mr Cameron did not break any rules and his office said the taxpayer had not lost any money.
The Telegraph also features an ICM poll which suggests more people intend to vote Liberal Democrat than Labour in the next general election.
The survey put Gordon Brown's party in third place for the first time since 1987 on just 22% - three points behind the Lib Dems and 18 behind the Conservatives.
'In a mess'
In response to public anger over MPs expenses, Foreign Secretary David Miliband has called for a "new approach to politics".
The foreign secretary wrote in the News of the World that British politics was "in a mess" and needed shaking up.
An elected House of Lords and greater powers for local communities were essential to make politics "more accountable, more in touch, less elitist", he said.
"'Never waste a crisis' is a good guide to getting out of a mess. And British politics has got into a mess," he wrote.
"At just the time when our problems need a new approach to politics, the expenses scandal has given people good reason to give up on politics altogether."
'Bread and butter'
But it was crucial to turn the anger into real change, he said.
"We have to start with expenses. Personally I don't care what system we have so long as it is clear, open and credible with the public - and we have to get it done quickly.
"But we can't stop there. Some people have said that constitutional reform is a 'middle-class issue', whatever that is. That's rubbish.
"We can't tackle the bread-and-butter issues unless our politics is more accountable, more in touch, less elitist."
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