The Ministry of Defence is facing fresh security questions after admitting that 658 of its laptop computers had been stolen over the past four years - nearly double the figure previously claimed.
The department also said that 26 portable memory sticks containing classified information had been either stolen or misplaced since January.
The Lib Dems condemned the latest security breaches - which happened despite a desperate cross-Whitehall drive to tighten procedures - as evidence of "shocking incompetence".
However, the MoD insisted that its policies were "generally fit for purpose", and said all data losses were fully investigated.
The embarrassing new details were disclosed by ministers in response to questions tabled in Parliament.
Previously the MoD had confessed to 347 laptops being stolen between 2004 and 2007.
But Defence Secretary Des Browne was forced to issue revised figures after "anomalies in the reporting process" were discovered. The official total is now 658 laptops stolen, with another 89 lost. Just 32 have been recovered.
In a separate response, ministers said that 131 of the department's USB memory sticks had been taken or misplaced since 2004. Some 26 of those went this year - including three which contained information classified as "secret" and 19 which were "restricted".
Lib Dem frontbencher Sarah Teather said: "It seems that this Government simply cannot be trusted with keeping sensitive information safe."
The MoD said it was taking steps to tighten security procedures.
