Chair of inquiry begun almost six years ago says no witnesses are taking unreasonable time to respond

Almost six years after he was given the job of chairing the official inquiry into the 2003 British invasion of Iraq, Sir John Chilcot continues to refuse to give a deadline for his report’s publication – though he has said he is making significant progress.

The three-year delay to the report has caused intense frustration inside Downing Street, with the cabinet secretary, Sir Jeremy Heywood, having offered the inquiry extra resources to speed up the process.

But in a letter to the foreign affairs select committee published on Friday, Chilcot said he was making significant progress in the process of “Maxwellisation” – the method by which witnesses likely to be criticised in the report are given a further chance to rebut potential criticisms of their behaviour.

He said none of the witnesses were taking an unreasonable length of time to reply but that once responses had been received the committee needed to evaluate them carefully.

Chilcot wrote: “Those involved in Maxwellisation process have engaged fully and I continue to judge that no one has taken an unreasonable length of time to respond given the range and complexity of the issues under consideration.”

He said he had given witnesses a reasonable but not indefinite amount of time to respond and the judgment on what was reasonable depended on individual circumstances.

David Cameron said recently he was fast losing patience over the lack of progress.

Speaking to the public administration select committee on Tuesday, Heywood said there was nothing he could do to accelerate the process, but insisted he had offered Chilcot extra resources when the pair met at the prime minister’s request at the beginning of July.

Heywood said: “I’m not washing my hands of it. It is an independent inquiry, the timetable is not in my hands.

“I have repeatedly offered to Sir John extra resources on behalf of the prime minister; extra legal resources and so on. At the prime minister’s request I saw him again recently, we had a private meeting at which I repeated that request, obviously.”

He said that when extra help had been offered, the inquiry team said it wasn’t needed and they were working as fast as they could.

“I just know that John Chilcot will complete this report as soon as he possibly can. He is as aware as everybody else is about the importance of getting this done and quickly.”