Communities and Local Government admitted its officials had "not fully" complied with guidance on handling sensitive data.

The department's top civil servant, Peter Housden, said in a statement: "It is clear that papers have been sent to Hazel Blears in a way that is not fully consistent with the departmental guidance."

He insisted "no damage had been done" because the documents were not "classified as secret or top secret".

Mr Housden added: "In any event, the computer was password-protected. I have instructed my officials that departmental procedures, guidance, and the awareness and accessibility of that guidance are now strengthened to ensure this does not happen again.

"I take full responsibility for ensuring this is done."

Department sources indicated that no officials were likely to lose their job over the blunder, but did not rule out disciplinary action.

Aides to Ms Blears said the computer was taken from her constituency office at Salford's Working Class Movement Library on Saturday.

The PC is believed to have contained several restricted Government documents - including one on the housing market from March.