The Foreign Secretary, David Miliband, angered critics of the Iraq war yesterday when he indicated that a long-awaited inquiry into the planning and execution of the conflict, promised by the Prime Minister, would be held behind closed doors.

He told MPs that the inquiry would be approved "as soon as practicable" once most British combat troops had returned home at the end of July. He admitted there were "important lessons to be learnt" from how the campaign was planned and carried out. But Mr Miliband also suggested its proceedings should be held in secret, similar to the Franks inquiry into the Falklands War. He said a private inquiry – proposed by the Conservatives – would prevent leaks, preserve the privacy of troops involved and enable those overseeing the investigation to see confidential Cabinet papers.

"It would preserve confidentiality that's very, very important for all of our troops," he said. "The fact that [Franks] was conducted in private meant it had access to all the relevant papers. Franks was not a judicial inquiry so it did not require its witnesses to have lawyers. There were no leaks or interim findings to distract from the final conclusions and recommendations of the inquiry."