The taxpayer has been landed with a £473,544 bill for the hunt for the missing HM Revenue & Customs data discs.
The Metropolitan Police Service mounted a months-long search for the data discs, containing 25 million child-benefit records, after they went missing in October 2007.
Financial minister Jane Kennedy revealed the costs in a written answer to Parliament.
The Metropolitan Police Service has said it will try to recover the full costs from HM Revenue & Customs (HMRC) for what is thought to be the most expensive lost-property inquiry ever in the UK.
The search for the discs was wound down in January, with an expectation that the discs will probably never be recovered.
At the investigation's peak, 47 detectives from the Specialist and Economic Crime Command took part in the hunt.
Police are believed to have searched National Audit Office buildings, two HMRC premises and other government buildings, the Royal Mail depot in Belfast, four TNT depots and a rubbish tip in Kent, with the main search concluding on 5 December, 2007.
The revelation was made in the wake of figures showing that Paul Gray, chairman of HMRC at the time the discs went missing, received a payout of £137,591 on quitting last November.