A memory stick containing passwords for a UK government services Web site where members of the public register to complete their tax returns has been found in a pub car park after being lost by contractor Atos Origin.
The Government Gateway, which is used by the public to access dozens of public services, including tax and benefit claims, was temporarily shut down after the loss.
The memory stick was lost by an employee of Atos Origin, which runs the site, before being found in a pub car park in Staffordshire. The vendor says the employee removed the device from its premises in "direct breach" of its rules and will be disciplined.
Atos Origin says it takes responsibility for the loss and is now working with the government and police.
The Department for Work and Pensions says the stick contained the passwords and encrypted personal data of a "handful" of people. Neither the site nor members of the public have had their security compromised, says the DWP, which has ordered an investigation into the incident.
The prime minister, Gordon Brown, told reporters Atos Origin would have "to explain itself".
The loss is the latest in a long line of data breaches involving government departments and cabinet secretary Gus O'Donnell is sending new instructions to ministers on handling sensitive information.
Last year computer discs containing the confidential information - including bank account details - of all 25 million child benefit recipients in the UK were lost by HM Revenue and Customs.