A Home Office laptop computer with a confidential encrypted disc was sold on eBay to a member of the public who discovered the disc when he sent the unit for repairs, say news reports.
Police are now investigating.
Lee Bevan of Leapfrog Computers, Manchester, told Sky News that the owner had brought the laptop in for repairs. When they opened the keyboard they discovered a disc that was marked "Home Office" and "Confidential".
A Home Office spokeswoman said the laptop was lost four years ago. She said there was no reason to suspect the loss had led to a data breach because the disc was encrypted.
She declined to say what the disc contained, what other data was on the laptop or whether the laptop was reported missing, saying she would comment further once police had finished their investigation.