MPs were allowed to claim millions of pounds in expenses last year without providing proof of entitlement, it has been disclosed.
On another hugely embarrassing day for the House of Commons, the Auditor General refused to sign off its accounts in full because of concerns about the "regularity" of payments to MPs.
Amyas Morse, the head of the National Audit Office, said he could not confirm the validity of £13.9 million of claims because he was unable to inspect supporting documentation.
The cash was claimed for and paid out mainly in the period between the eruption of the expenses scandal in May 2009 and this year's general election.
The Commons Members' Estimate Committee, which oversees House finances, admitted that "checks and balances were not adequate". Campaigners said the disclosures were further proof that MPs remained out of touch with the electorate.
The Commons is now trying to claw back more than £33,000 from a number of unidentified MPs who were either paid expenses by mistake or could provide no evidence at all that the transactions were even made.
But the sums being chased are a fraction of the amount questioned by Mr Morse and about half may have to be written off anyway because the MPs have since quit parliament.
The Auditor General's initial discoveries of missing documentation prompted an 11-month "remedial" project by the House to try to retrospectively obtain evidence for claims.
But £830,000 remained entirely unsupported at the end of that process in October. Of that, £460,000 related to MPs' staffing budgets and £370,000 to second homes and offices.
Support could not be provided for another £1.8 million of claims because the MPs concerned were under investigation by the police.