A computer has been stolen from the constituency office of Communities Secretary Hazel Blears, it was revealed today.
The machine contained material from the Department for Communities and Local Government and details relating to her constituency work.
It was taken from her office in Salford's Working Class Movement Library on Saturday.
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."
The Shadow home secretary Dominic Grieve 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."
The Liberal Democrat home affairs spokesman Chris Huhne 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."
Last week a Cabinet Office official was suspended and an investigation launched after secret papers featuring details of al-Qa'ida and security in Iraq were left on a train.
And the Home Secretary Jacqui Smith is to be called before the Commons Home Affairs Select Committee after Treasury papers relating to plans to tackle funding for global terrorism were also found on a train.