MPs demanded a "cultural change" in public-sector data handling yesterday as it emerged a computer hard drive possibly containing the private details of armed forces personnel was missing.

In the latest Whitehall data embarrassment, the Ministry of Defence said its IT contractor, Eds, could not account for the portable hard drive.

It could contain the names, addresses, passport numbers, dates of birth, next of kin and driving licence details of up to 100,000 Army, Navy and RAF personnel.

An urgent investigation by the MoD is under way to establish what the drive actually contains. Officials stressed 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".

It is only the latest information security breach to hit the MoD. In July it admitted 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.

Tory MP Nigel Evans, who chairs the All-Party Parliamentary Group on Identity Fraud, said: "This is yet another example of the serious implications the loss of personal data can have for the general public. The fact that it has been revealed during National Identity Fraud Prevention Week is ironic.

"The loss of such important information including bank details, passport numbers and dates of birth will be music to the ears of fraudsters everywhere.

"It is vital that there is a cultural change across the public sector with all professionals aware of their responsibility to protect and manage personal data."

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

LibDem defence spokesman, 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."

An MoD spokeswoman said: "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.

"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."

Meanwhile, it was also revealed yesterday that a laptop containing data on around 100,000 pensioners was stolen last month.

The computer, which contained pensioners' names, National Insurance numbers and salary details, was in a handbag snatched from an employee of accounting firm Deloitte.

Deloitte said the machine was protected by security measures, and there was only a "very, very low" risk of anyone being able to access the data.

Deloitte said it had notified police of the theft, and informed its clients, who in turn have contacted all of the pensioners whose data was on the laptop. No address or bank account detail was stored on the machine, the company said.

The company said the theft had happened despite employees being issued with guidelines to pay close attention to their laptops in public places.