Elliot Morley has been suspended from the Parliamentary Labour Party
There are growing calls for a police investigation into some of the MPs' expense claims revealed by the Daily Telegraph newspaper.
The TaxPayers' Alliance has complained to police about former minister Elliot Morley, who claimed £16,000 for a mortgage he had already paid off.
The campaign group has warned it would consider a private prosecution if the authorities fail to act.
Scotland Yard said no decision had been taken on whether to investigate.
The Taxpayers' Alliance has joined forces with the Daily Mail newspaper to raise funds for private criminal prosecutions of MPs they believe have a case to answer.
The fund will be used if the police decide not to launch an investigation into the alleged misuse of parliamentary expenses.
Mark Wallace from the campaign group said it was important that the worst cases were properly investigated.
He told BBC News: "The Taxpayer's Alliance is absolutely committed to taking action on this issue.
"We've already spoken to the police about requesting an investigation and, I've got to say, if the police drop the ball and if we think it's a better alternative, we may well be going for a private prosecution, that's something we're taking extremely seriously."
He said people were appalled MPs thought they could rectify the situation by simply paying back the money that had been wrongly claimed.
We have received and are currently considering a number of complaints in relation to alleged misuse of expenses
"If somebody burgles a house and they take a television and they are caught, they can't say to the police, 'Oh, I'm terribly sorry, I'll give the television back,' and the police don't say, 'Oh well, that's fine then.'
"This is about having clear justice and I think we'll be investigating the cases that have come out, the cases that are still to come out and all of those receipts in a lot of detail."
The independent Mayor of Middlesbrough, Ray Mallon, said he had also written to the Metropolitan Police Commissioner, Sir Paul Stephenson, asking him to investigate the revelations.
Mr Mallon said he was responding to complaints from members of the public and was also acting in his capacity as a taxpayer.
He said: "As homes are being repossessed up and down the country it appears that some MPs have been secretly manipulating the system to help pay off mortgages, dodge taxes and increase the value of their homes at the expense of the taxpayer.
"The guidelines for all MPs say claims should not be made unless they are 'above reproach' - clearly some of these claims have gone way beyond that and may have crossed into criminality."
On Thursday evening London Mayor Boris Johnson suggested the police could have reason to investigate the claims made by some MPs.
"Frankly, looking at some of these cases it looks to me as though Plod needs to come in," he told Sky News.
"I must be careful what I say here because I am chairman of the Metropolitan Police Authority, but it looks to me as though some people may very well have a serious case to answer."
A Scotland Yard spokesman said: "We have received and are currently considering a number of complaints in relation to alleged misuse of expenses, but no decision has been taken on whether to investigate."
A Conservative councillor in Bedfordshire says he has asked the police to investigate a claim made by the Labour Luton MP Margaret Moran in relation to a home in Southampton.
Richard Stay wrote on his website: "Every MP is required to sign a form that says that any expense claimed from the tax payer is incurred wholly and necessarily to enable them to carry out their parliamentary duties.
"I will be intrigued to see how Ms Moran, the less than honourable member for Luton South, explains how her declarations square with the reality of £22,000 worth of dry rot at her seaside home."
Ms Moran released a statement in response to the suggestion the police had been asked to investigate her claim.
She said: "I do not feel I have done anything wrong. I have given the money back and the fees office has apologised for giving me the wrong advice.
"As for what happens next, I will take my guidance from my constituency party, who are standing by me."