The police investigation into abuses of parliamentary expenses has cost more than £840,000, Scotland Yard has said.
Up to 13 officers have been working on cases since the scandal broke in May 2009, according to the response to a freedom of information request.
Former Labour MPs David Chaytor, Eric Illsley and Jim Devine, and former Tory Lord Taylor of Warwick have been convicted of fiddling expenses.
The costs of bringing the prosecutions are not yet known.
In response to a freedom of information request from the Press Association, Scotland Yard said its bill up to the middle of January was estimated at £840,000.
A spokesman said: "There have been up to 13 police officers employed on the MPs' and Lords' expenses inquiry between May 2009 and the middle of January 2011, which is the most up-to-date financial information available.
"No costings are available per case investigated. Not all the officers have been employed on a full-time basis.
"They have worked on a case-by-case basis and as the need has arisen. The time they have spent doing it has been costed on the basis of the percentage that they have dedicated to this inquiry."
Mr Chaytor was sentenced to 18 months in prison in January, while Mr Illsley was jailed for 12 months in February.
Lord Taylor and Mr Devine are awaiting sentencing.