A complaint about former Labour minister Denis MacShane's expenses claims has been referred to the Metropolitan Police.
A parliamentary investigation into the complaint has been suspended "until the question of possible criminal proceedings has been resolved".
Former Europe minister Mr MacShane has been suspended from the Parliamentary Labour Party in the meantime.
He said he regretted the development but would co-operate with police.
Parliamentary Commissioner for Standards John Lyon had been investigating a complaint made against Mr MacShane, MP for Rotherham, over a year ago.
But on Thursday the Commons Standards and Privileges Committee, which oversees Mr Lyon's work, said it had agreed that he should report Mr MacShane's conduct to the Metropolitan Police and suspend his investigation in the meantime.
Mr MacShane said the complaint had been filed against him in June 2009. He added: "While I obviously regret this development I will of course co-operate fully with the police as I have with the commissioner. I will make no further comment."
A Scotland Yard spokesman said he could "confirm that the Metropolitan Police Service has received a referral from the Parliamentary Commissioner for Standards relating to parliamentary expenses."
It would be considered "along with a small number of other allegations" relating to MPs expenses, he said.
The Labour Party confirmed it had "suspended Denis MacShane from the Parliamentary Labour Party and the whip pending the outcome of any investigation".
Three former Labour MPs - Elliot Morley, David Chaytor and Jim Devine - current MP Eric Illsley and former Conservative peers Lord Taylor and Lord Hanningfield have all been charged with offences related to their expenses claims.
The expenses row dates back to the publication last year - following leaks to the Daily Telegraph - of thousands of claims by MPs, which came after a lengthy Freedom of Information battle.