Gordon Brown was forced into a partial U-turn yesterday over his decision to hold a secret inquiry into the Iraq War, conceding that some parts of it could be open to the public.

The Prime Minister changed his mind after an angry reaction to his announcement in the Commons on Monday that Sir John Chilcot, a former senior civil servant, would conduct his inquiry behind closed doors.

In a letter to Sir John, Mr Brown gave him the option of allowing witnesses to take a legal oath and appear in private or public. “It is essential that all those appearing before the inquiry do so with the greatest possible candour and openness and that the inquiry itself proceeds as efficiently as possible while maintaining full public confidence in the integrity of the process and without in any way damaging national security,” he wrote.

Mr Brown said that he expected Sir John to consult opposition leaders and relevant select committees before setting out how he would conduct the inquiry.

Conscious of the furious response from some of the families of soldiers killed in Iraq, he added: “It is also essential that the families of those who gave their lives in Iraq are properly consulted on the nature of the inquiry. I hope, therefore, that you will be able to meet them as part of the preparations and as you continue your work, to explain how you are proceeding. This could be, at their request, in public or private.”

Senior Whitehall officials expressed dismay that the issue had been mishandled. Even the service chiefs at the Ministry of Defence appeared to be at loggerheads over the status of the inquiry.

The MoD said that before the announcement by the Prime Minister in the Commons, Downing Street had consulted Bob Ainsworth, the Defence Secretary, and John Hutton, his predecessor.

Sir Bill Jeffrey, the MoD’s Permanent Under Secretary, and Air Chief Marshal Sir Jock Stirrup, the Chief of the Defence Staff, were also consulted.

A spokesman insisted that Sir Jock had informed the three service chiefs, including General Sir Richard Dannatt, the head of the Army. But it seems there was no separate consultation between Sir Jock and the service chiefs on how the inquiry was to be conducted.

This is what is behind General Dannatt’s complaint in a BBC radio interview that he had not been “consulted” over whether the inquiry should be held in public or in private. He made it clear that he favoured parts of the inquiry being conducted in public.

Opposition to a private inquiry gathered pace yesterday. Sir John Major, the former Conservative Prime Minister, said that the decision was inexplicable.

The Commons Public Administration Committee said there was a “strong risk” that the inquiry as constituted would not be able to establish the truth. It urged the Prime Minister to allow a free vote in the Commons on the proposal.

Lord Butler of Brockwell, the former Cabinet Secretary who in 2004 headed the review of intelligence behind the decision to invade Iraq, told peers: “I reluctantly conclude that the form of the inquiry proposed by the Government has been dictated more by the Government’s political interest than the national interest and it cannot achieve the purpose of purging mistrust.”

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