Among the more high profile examples is the case of Gulf War invasion plans stored on a computer stolen from an RAF officer’s car in 1990.

Another came to light in 2004, when highly confidential details of the new identity planned for Soham killer Ian Huntley’s ex-girlfriend Maxine Carr were stolen from a civil servant’s car as she celebrated a friend’s birthday in a pub.

Here are other cases to emerge in the recent past:

JULY 2008: MEMORY STICKS AND LAPTOPS

The Ministry of Defence confirmed that 121 computer memory sticks and more than twice as many laptops than previously thought have been lost or stolen in the past four years.

Armed Forces Minister Bob Ainsworth gave a written statement to parliament saying 121 USB memory devices had gone astray – five of which contained secret data.

And in a parliamentary written answer, Defence Secretary Des Browne said 747 laptops had been stolen – 400 more than originally reported. Of those, 32 have been recovered so far.

JUNE 2008: TERROR DOCUMENTS

A senior intelligence officer from the Cabinet Office was suspended after documents were left on the seat of commuter train from London Waterloo. A passenger later handed them to the BBC.

The seven-page file, classified as “UK Top Secret”, contained a report entitled “Al-Qaeda Vulnerabilities” and an assessment of the state of Iraq’s security forces.

Cabinet Minister Ed Miliband said there had been a “clear breach” of security rules, which forbid the removal of such documents from government premises.

But Mr Miliband said national security did not seem to be “at risk”.

Two inquiries – one by the Cabinet Office, the other by the Metropolitan Police – have been launched.

APRIL 2008: MCDONALD’S LAPTOP

An Army captain’s laptop was taken from under his chair as he ate in a McDonald’s, near the Ministry of Defence’s Whitehall headquarters.

The MoD said the data on the laptop was not sensitive, and was fully encrypted.

This is the latest MoD laptop theft to be made public and it came after the government tightened the rules on employees taking computers out of work.

Whitehall staff are now banned from taking unencrypted laptops or drives containing personal data outside secured office premises.

JANUARY 2008: MILITARY RECRUITS

A laptop computer belonging to a Royal Navy officer was stolen from car in Edgbaston, Birmingham.

It contained the personal details of 600,000 people who had expressed an interest in, or applied to join, the Royal Navy, Royal Marines and the RAF.

It contained data including passport numbers, National Insurance numbers and bank details.

Defence Secretary Des Browne later admitted the inquiry into the loss of the Royal Navy officer’s laptop uncovered two similar thefts since 2005.

At the time, Dr Liam Fox, shadow defence secretary, said 68 MoD laptops had been stolen in 2007, 66 in 2006, 40 in 2005 and 173 in 2004.

DECEMBER 2007: DRIVING TEST CANDIDATES

The details of three million candidates for the UK driving theory test went missing in the US.

Names, addresses and phone numbers – but no financial information – were among the details stored on a computer hard drive, which belonged to a contractor working for the Driving Standards Agency.

The information was sent electronically to contractor Pearson Driving Assessments in Iowa and the hard drive was then sent to another state before being brought back to Iowa, where it went missing.

Ministers said the information had been formatted specifically to meet the security requirements of Pearson Driving Assessments and was not “readily usable or accessible” by third parties.

NOVEMBER 2007: CHILD BENEFIT RECORDS

HM Revenue and Customs (HMRC) lost two computer discs containing the entire child benefit records, including the personal details of 25 million people – covering 7.25 million families overall.

The two discs contained the names, addresses, dates of birth and bank account details of people who received child benefit. They also included National Insurance numbers.

They were sent via internal mail from HMRC in Washington, north-east England, to the National Audit Office in London on 18 October, by a junior official, and never arrived.

The Metropolitan Police were informed of the loss in November and extensive searches began.

In December, a reward of £20,000 was offered for the return of the two discs, but they were never recovered.