Tory MPs have been urged to explain their conduct to their constituents
Conservative MPs who have abused the expenses system must face "retribution" and be deselected, one of the party's leading donors has said.
Lord Kalms, a former Conservative Party treasurer, said the behaviour of some MPs had been "outrageous" and those at fault should "pay the penalty".
A handful of Tory MPs criticised for their expenses claims have said they will not stand at the next election.
Bromsgrove MP Julie Kirkbride is under mounting pressure over her position.
The Tory leadership says Ms Kirkbride still has "questions to answer" amid claims she paid her sister £12,000 to do clerical work for her constituency office even though she lives more than 100 miles away in Dorset.
Ms Kirkbride has defended her actions but faces opposition in her constituency where thousands of people have signed a petition calling on her to stand down.
Her husband, Tory MP Andrew MacKay, is standing down from Parliament at the next election after criticism of the couple's second home expenses claims.
Tory leader David Cameron has said all his MPs must be prepared to defend their expenses claims to their constituents and has urged MPs to hold public meetings to explain their conduct.
Any MP who refuses to co-operate with an internal scrutiny panel or pay back claims deemed to be excessive or inappropriate faces losing the whip.
Lord Kalms said all Tory MPs with question marks over their claims "should put the facts before their constituents".
But he told BBC Radio 4's World at One programme that this would not be enough to save those MPs who had "seriously breached" the rules and would have to face "retribution" for their actions.
"Some of the claims were so outrageous as to be an abuse of the system," he said.
"We don't have all the information at this stage, only the worst examples. If there are other examples even near that, I would say they would exclude people from being in Parliament in the future."
Mr Cameron would have to make "some major decisions" about the future of some MPs, Lord Kalms added, although he refused to be drawn on individual cases.
But he said practices such as flipping - by which some MPs changed the designation of their second home in order, it is alleged, to maximise their allowances - were "horrendous".
It was not enough for MPs to say they were acting within the rules as they stood, he stressed, as it showed a "total lack of ethical behaviour and total lack of integrity".
"All of the people who have taken advantage of these opportunities must now pay the penalty," he said.
Lord Kalms' comments came as the Labour's own scrutiny panel began its process of judging whether some of the party's MPs should be barred from standing at the next election.