Hazel Blears could face disciplinary action after she ordered sensitive Cabinet documents on religious extremism to be forwarded to a laptop in her constituency, which was subsequently stolen.

Downing Street said that an “urgent” investigation was under way after the documents relating to security and planning were e-mailed from secure government machines to the computer in Ms Blears’ Salford constituency office in Salford’s Working Class Movement Library.

Last week a senior Cabinet Office official was suspended for leaving top secret documents on a train. The Prime Minister was informed of the loss, and ordered Cabinet yesterday to ensure that procedures on sensitive information were enforced.

The Conservatives said Ms Blears, the Secretary of State for Communities and Local Government, had committed an offence under Section 8 of the Official Secrets Act, which makes it an offence if they “fail to take such care to prevent the unauthorised disclosure of the document or article as a person in his position may reasonably be expected to take”. This could pave the way for a police investigation into her conduct.

A Tory source said: "There would be grounds for a police inquiry into this. The idea that restricted documents are not something to be concerned about is wrong. Restricted documents are covered by the Official Secrets Act."

The machine contained a combination of constituency and government information which should not have been held on it.

The stolen computer is understood to have contained Cabinet papers about extremism and a document outlining the views of various members of the Cabinet on the new planning commission. The existence of a document outlining divisions on the issue of planning ahead of next week’s crucial vote will alarm ministers.

The documents did not contain any information that could compromise national security.

A Government spokesman stressed that no personal details were among the departmental information.

“There was a break-in at the constituency office of Hazel Blears on the afternoon of Saturday, June 14. Hazel was not there at the time,” a spokesman said.

“The thief broke in through a window, triggering the building’s security alarm. A PC (personal computer) was stolen. Nothing else was taken.

“We understand the building’s security staff arrived within minutes. The PC was primarily used for Hazel’s constituency business and contained some details of her constituency work.

“The PC also contained some material from the department. None of the departmental material included sensitive personal data about the public or would be of use to criminals. The PC did not contain any secret or top secret information and the contents of the PC are protected and clearly this is now subject to a routine police investigation.”

Manchester Police are investigating the theft from the office in Salford’s Working Class Movement Library on Saturday. Nothing else was taken.

A spokesman for Greater Manchester Police said: “Shortly after 5.45pm on Saturday, June 14 2008, police were called to the Working Class Movement Library on The Crescent, Salford, following reports of a burglary. Officers attended and discovered an office had been broken into. Inquiries are continuing.”

Dominic Grieve, the Shadow Home Secretary, said: “The news that a Government minister may have been directly responsible for the loss of data relating to extremism is extremely alarming. It comes after a series of security breaches over which Government appears not to have regained control.

“The Government must urgently clarify what happened in this case. If Hazel Blears has breached security rules in relation to material she has handled, Parliament must be told exactly how and why this has occurred.”

Chris Huhne, the Liberal Democrat home affairs spokesman, said: “Cabinet ministers have just ticked off their civil servants about security lapses, but now Hazel Blears shows that the rot starts at the top. This is the third breach of secrecy in a week. The Government has to get a grip on the slap-dash culture of sloppiness that threatens national security.”

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