Also on the portable hard drive was data on 600,000 potential applicants to the armed forces and the names of their referees, in the latest in a string of embarrassing data losses by the government in the past year.

"On Wednesday, October 8 we were informed by our contractor EDS that they were unable to account for a portable hard drive used in connection with the administration of Armed Forces personnel data," a spokeswoman said.

She added that MoD police were investigating the data loss.

On the hard drive were the names, addresses, passport numbers, dates of birth and driving license details of about 100,000 serving armed forces personnel spread across the three services -- the army, navy and air force -- as well as their next-of-kin details.

Defence officials did not rule out that bank account details of serving personnel were also held on the drive.

Overall, the total personnel strength of the MoD is around 282,600, of which about 193,100 is military personnel, according to the ministry.

The government has been hit by several revelations of major data losses in the past year, the most recent of which was the news last month that thieves had stolen the personal records of thousands of current and former Royal Air Force staff from a base in western England.

Last November, the government admitted it had lost confidential records for 25 million Britons who receive child benefit payments, and in January, the defence ministry revealed that a laptop with details of some 600,000 people interested in joining the armed forces had been stolen from a naval officer.

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