The Metropolitan police's attempt to use the Official Secrets Act to force a Guardian reporter to reveal her sources has been condemned by the chairman of the Commons' home affairs select committee, Keith Vaz.

Following a private meeting with Deputy Assistant Commissioner Mark Simmons, Vaz, a Labour MP, criticised officers' failure to seek external legal advice before resorting to the courts to obtain notes about phone-hacking stories.

"I consider it was a mistake that they did not use senior counsel in the first place and that the Official Secrets Act was used in these circumstances," Vaz said. "It was right to withdraw the proceedings against The Guardian." The "informal, private" session, at which Vaz was the only MP present, was held behind closed doors.

Parliament is in recess during the party political conference season; notes were taken and will be circulated to other members of the committee.

"I met with Mark Simmons and members of his team this afternoon," Vaz added in his statement. "They gave me a full explanation as to the events that led to the use of the Official Secrets Act against the Guardian.

"The matter is now the subject of an ongoing investigation. It is imperative that the integrity of Operation Weeting [the police investigation into phone hacking] is maintained.

"I have informed the Metropolitan police that the committee will be raising the issue with the new commissioner, Bernard Hogan-Howe, when he appears before us on 11th October."

Vaz said that he had also written to Alan Rusbridger, editor-in-chief of the Guardian, seeking clarification of the newspaper's version of events.

Detectives' attempts to use the Official Secrets Act to force the Guardian's reporter Amelia Hill and the newspaper to reveal the sources behind the revelation that Milly Dowler's phone had been hacked by the News of the World has raised a furore over threats to media freedom.

The Met abandoned the move earlier this week after consulation with the Crown Prosecution Service. The Director of Public Prosecutions, Keir Starmer QC, revealed that he had not been consulted in advance.

Vaz's decision to hold his meeting with the Met had in turn been criticised for being held behind closed doors. John Kampfner, chief executive of Index on Censorship, said that it was: "... a damaging move for parliament and the Metropolitan police. It is important that the police explain their actions openly.

"The attempt to use the Official Secrets Act on a journalist was an outrageous attack on free speech and those responsible should explain themselves not just to parliament but to the country."

In a letter to the Guardian on Friday, Vaz defended his decision. "Arrangements for a full-scale committee hearing on this issue at this time would not be practicable in the middle of the conference season," he explained.

The powerful home affairs committee is in the process of investigating hacking and has lambasted the Met for its failures to pursue inquiries.