The discovery of secret documents detailing anti-terror plans for Heathrow Airport at a roadside is the latest in a catalogue of errors surrounding highly sensitive security documents.
BBC News Online looks at other instances when Whitehall and intelligence services officials have lost sensitive documents.
May 2004: Highly confidential details of the new identity planned for Soham killer Ian Huntley's former girlfriend Maxine Carr are stolen from a civil servant's car as she celebrates a friend's birthday in a north London gastro-pub.
July 2003: It emerges six laptop computers have been stolen from Whitehall - three of them from the Cabinet Office.
June 2002: Home Secretary David Blunkett's own security details - including aerial photographs of his home, instructions for the alarm system, and his daily routines - are found outside the Woodseats Palace pub, in Sheffield, in an 11-page dossier marked "Confidential. Not to be copied" .
May 2002: A laptop computer containing secret information about Britain's air-to-air missile system is found in a skip outside the offices of MBDA Missile Systems in Stevenage, Hertfordshire.
Documents on the hard-drive also reveal Nato fears about delays in replacing Tornado jets with the new Eurofighter, and details of arms sales to Spain, Pakistan and several Middle East countries.
May 2002: The Daily Mirror newspaper is given a Ministry of Defence (MoD) laptop containing sensitive information intended to be read only by the prime minister, the head of the civil service and defence chiefs.
January 2002: It is revealed 1,933 government computers have been lost or stolen, and a crackdown is ordered to tighten laptop security.
April 2001: An MoD worker makes a frantic call to Scotland Yard after leaving a £1,700 Dell laptop, containing details of new weapons systems, in a taxi he has taken from Waterloo train station.
December 2000: Police conduct an exhaustive search of scores of trains and stations after a MI5 agent leaves a briefcase full of intelligence secrets on a train in Dorset.
March 2000: Spy chiefs take out newspaper advertisements offering a "substantial reward", after an MI6 operative leaves his computer in a taxi after drinking at a tapas bar in Pimlico, central London.
March 2000: An MoD laptop containing sensitive files on Northern Ireland is stolen from a MI5 officer at Paddington station in London.
March 2000: Thieves break into the home of the armed forces minister, John Spellar, in Bromley, Kent, and steal his computer but leave without touching boxes containing highly sensitive defence and nuclear information.