Any MPs who committed a crime by claiming taxpayer-funded cash for non-existent mortgages should "face the full force of the law", Tory leader David Cameron has said.
He said Scotland Yard, which is considering whether to launch criminal inquiries into potentially fraudulent claims, should examine them "without fear or favour".
It came as Labour former minister Elliot Morley became the latest MP to end his Commons career over the scandal, announcing he would not fight his Scunthorpe seat at the next general election.
Mr Morley claimed more than £16,000 in interest payments on a home loan that had already been paid off but insisted he would clear his name over what had been an honest mistake.
"If people have broken the law in claiming expenses, like mortgage payments for mortgages that don't exist, should they be subject to the full force of the law? Yes of course they should," Mr Cameron told The Daily Telegraph, which has exposed detailed Westminster expense claims.
"I've said it's not for me to call in the police but the police know what the law is and if they feel it's been broken they should be able to look at that without fear or favour."
Mr Cameron said he was "ashamed" at what some of his and other parties' MPs had done and accepted it had damaged his party.
"Has this been a setback for the Conservative Party? Yes. The sight of people claiming for duck ponds and moats and pools is a bad sight. I am ashamed by what's happened. You have the sort of fastidiousness of ministers hiring accountants to fill in their tax returns and getting the taxpayer to pay for it. It never occurred to me that people would or could do that.
"But also, like others, the swimming pools, the moats, the duck ponds. The lack of common sense and reasonableness has been shocking."
He also praised Julie Kirkbride, who announced she would quit the Commons after a public and media storm over her expense claims, for attempting to publicly defend herself. And he urged others, including Prime Minister Gordon Brown, to face local activists.
