Sir John Chilcot is facing legal action from the families of Iraq War soldiers for failing to provide a deadline on when he will finally publish the delayed report into the conflict.
Families claim Iraq Inquiry chairman Chilcot has acted unlawfully by refusing to say when the report will be published six years after it was launched at a cost to taxpayers of around £10m ($15.5m, €14m).
Prime Minister David Cameron has said he and the British public is "fast losing patience" with the five-member panel, which was expected to publish its report three years ago but claims delays have been in order to give those criticised time to defend themselves.
But patience the patience of 29 families has worn thin and their lawyers have written to Chilcot threatening to take their case to the High Court unless the report is produced by the end of the year - 12 years after the US-led invasion begun.
Matthew Jury, one of the solicitors representing the families, told the BBC that delays caused further pain to the families. "This suffering has only been compounded over time," he said. "They describe it to me as a black cloud hanging over their heads and the only way to disperse that cloud, for them to get some degree of closure, is for this report to be published and for them to finally know the truth."
Last month Sir Jeremy Heywood, the cabinet secretary, claimed the inquiry chairman had refused extra help to speed up the publication. "We have repeatedly offered the inquiry extra resources, they say they don't need them – they are doing it as fast as they can," Heywood told the Public Administration and Constitutional Affairs Committee.