A British Defence Ministry laptop computer packed with national security secrets is missing after an official left it in the back of a taxi, the mass-selling Mirror tabloid says.

The laptop was thought to contain vital information about new weapons systems, it said.

The Mirror said the official had notified police about the missing laptop, but neither the Defence Ministry nor police would comment.

In March last year there were reports that agents of MI5, Britain's domestic security service, and MI6, the overseas service, had lost laptops containing secret information.