Gordon Brown faced accusations of a fix and an “Establishment stitch-up” yesterday after ruling that the long-awaited Iraq war inquiry would be in secret and not report until after the general election.

The Prime Minister came under attack from MPs on all sides, as well as from families of troops killed in the conflict, after insisting that hearings could not be held in public for reasons of national security.

He also surprised MPs by saying that the inquiry, by a committee of privy counsellors headed by a former Whitehall mandarin, would not seek to apportion blame. Critics said that the committee did not have enough military or political experience.

Mr Brown argued closed hearings would ensure evidence given to the inquiry by politicians, military officers, and officials would be as “full and candid as possible”. He also pointed to the experience of the long-running public inquiry by Lord Saville of Newdigate into the Bloody Sunday killings in Northern Ireland, which has yet to report after eight years.

His arguments were dismissed by the opposition parties, who warned that it would not satisfy public demands to establish the truth of what had happened.

David Cameron said it belied the promises given by Mr Brown only a week ago when he spoke of a “new era of democratic renewal”.

“The inquiry needs to be, and needs to be seen to be, truly independent and not an Establishment stitch-up,” he said. Mr Cameron said that with the inquiry timed to end after the election there was a danger the public would believe the process had been “fixed to make sure the Government avoids having to face up to any inconvenient conclusions”.

Nick Clegg, the Liberal Democrat leader, said he had held talks yesterday with bereaved relatives of Service personnel who had urged him to press for a full public inquiry. “A secret inquiry conducted by a clutch of grandees handpicked by the Prime Minister is not what Britain needs,” he said.

General Sir Mike Jackson, who was head of the Army from 2003 to 2006 during the most challenging period of the war in Iraq, said he was surprised that a senior retired judge had not been selected to head the inquiry, rather than a former civil servant.

“Apparently there’s to be no subpoena arrangement for witnesses to attend the inquiry because there is no legal status for it, so there’ll be no swearing to tell the whole truth and nothing but the truth,” General Jackson, now retired, told The Times.

He acknowledged that the Government was a facing a “no-win” situation with the announcement about a private inquiry. He said: “If you hold a public inquiry then you’re going to get lawyers, delay and probably economy with the truth, and if you make it private, you’ll get all the facts but people will feel it’s a cover-up.” he said.

Mr Brown’s pledge of an inquiry was seen as part of his efforts to regain the initiative after doubts over his leadership resurfaced in recent weeks.But he appeared to have upset Labour MPs who have been demanding an inquiry by his decision to go for an investigation similar to the Franks report after the Falklands conflict.

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