THOUSANDS of Westcountry armed forces personnel were on alert last night after it emerged that a crucial computer hard drive possibly containing their private details was missing.

Private contractors working for the Ministry of Defence admitted they could not account for the portable drive, which may contain the names, addresses, passport numbers, dates of birth, next-of-kin and driving licence details of up to 100,000 personnel from across the Royal Navy, RAF and Army.

It is the latest embarrassing data blunder to hit the Government, which has admitted losing hundreds of laptops, memory sticks, confidential reports and even disks containing the personal details of every family in the country.

Plymouth Devonport MP Alison Seabeck said she was "horrified" by the latest revelation, while Devon South West MP Gary Streeter called for a cross-Whitehall summit for the Government to "get a grip" on the problem.

An urgent investigation by the MoD is under way to establish exactly what the drive contains. Officials stressed that they were currently treating the case as a "potential" data loss.

Ministers are understood to be "furious" at the development and insistent that it is resolved as quickly as possible. Downing Street described the loss of the data as "regrettable".

The Liberal Democrats branded the news a "disturbing breach of security" and called for an urgent inquiry into how it had occurred.

Lib-Dem defence spokesman and North Devon MP Nick Harvey said: "This is extremely serious news and the immediate priority must be to ensure the security of all military personnel. However, once that has been established, there must be an urgent investigation into how such a disturbing breach of security could be allowed to happen."

Ms Seabeck said Government departments had been sending out clear messages about the handling of secure, sensitive information.

In July, the MoD admitted that 658 of its laptops had been stolen over the past four years and 26 portable memory sticks containing classified information had been either stolen or misplaced since January.

Mr Streeter told the WMN: "I think there needs to be some kind of summit meeting at Government level to sort this out because it is going on in every department.

"It is totally unacceptable and in relation to our armed forces, it could in some circumstances – if it fell into the wrong hands – be very damaging."

An MoD spokesman said the ministry was informed on Wednesday by contractor EDS that "they were unable to account for a portable hard drive used in connection with the administration of armed forces personnel data".

"This came to light during a priority audit EDS are conducting to comply with the Cabinet Office data handling review. The MoD Police are investigating this matter with EDS."