Defiant Iraq war inquiry chairman Sir John Chilcot today refused to publish his long-awaited report into the conflict – and revealed he was still pursuing new lines of inquiry.

Sir John insisted he understood 'the anguish of the families of those who lost their lives in the conflict', but said it was 'critically important that the report should be fair'.

He spoke out in the wake of mounting criticism over delays to his report with families of soldiers killed in Iraq threatening legal action and Prime Minister David Cameron expressing his frustration.

Defiant Iraq war inquiry chairman Sir John Chilcot today refused to publish his long-awaited report into the conflict – and revealed he was still pursuing new lines of inquiry

But breaking his silence this afternoon, Sir John said he had yet to receive responses from everyone he had criticised in his first draft of the report.

He also revealed that he would carry out further work on the report after receiving the responses.

Only then would he be able to give Parliament a timetable for when the report was likely to be published.

In his statement, Sir John said: 'I should like firstly to reiterate that my colleagues and I understand the anguish of the families of those who lost their lives in the conflict.

'We take the responsibility we were given as an independent inquiry extremely seriously, and understand the need for Government, Parliament and the public to see our report as soon as possible.'

But he added: 'It is critically important that the report should be fair to all who participated in the conflict and to those who bore the responsibility of taking decisions.'

Roger Bacon, whose son Major Matthew Bacon was killed in Iraq in 2005, said he was 'disappointed' Sir John Chilcot has not revealed when he will publish the Iraq report, adding: 'I'm not sure he is able to understand our anguish.'

Sir John's report is being held up by the so-called 'Maxwellisation' process which seeks responses from those who face criticism.

The Chilcot report into the Iraq war is expected to criticise establishment figures beyond Tony Blair and his inner circle

But the former international development secretary Clare Short today revealed that all of those criticised were asked to reply to the inquiry within a deadline of a few weeks which passed 'a long time ago'.

She claimed author Sir John was probably having to redraft the report as the current version is 'very poor'.

She also revealed that the report is set to criticise ministers across government up to and after the 2003 invasion as well as civil servants.

Ms Short told BBC Radio 4's World at One programme: 'It's not just politicians, the criticism seems to go right across Whitehall, senior permanent secretaries, the top of the civil service, everybody.

'I see it and think this means everyone's to blame, no one is to blame, we won't get a proper diagnosis and it won't be helpful in finding out what went wrong with our system.

Former international development secretary Claire Short is expected to be criticised in the report

'Any individual that's criticised only sees a part of the report and then gets a chance to comment on that part.

'That's the Maxwellisation (process) and there's a time limit for everyone to comment, so the suggestion that Maxwellisation is causing all the delay, I don't think is true.

'I think what might be true is that the draft is very poor and it's as big as War and Peace I understand, lots of people have made serious responses and they are probably having to redraft.

'But I think the hope of it being a good piece of work that Britain learns what went wrong and we don't do it again looks very, very poor to me.'

Ms Short claimed that Sir John and the inquiry panel were probably redrafting the report because it contains errors in the first draft, including in relation to her role as international development secretary from 1997 until just after the invasion of Iraq in 2003.

She said: 'Dfid is included in the criticism whereas in fact the department I think behaved superbly in preventing a humanitarian disaster, which there nearly was immediately after the invasion.

Lawyers acting for relatives of British soldiers killed in Iraq have given Sir John a 5pm deadline to announce when he will publish his report.

Matthew Jury, of McCue and Partners, which is representing 29 families, said they would proceed with legal action if the deadline is missed.

The delay in publication has been a growing source of frustration for the families as well as Mr Cameron, who has demanded a timetable for publication be set out ''pretty soon''.

The Chilcot report into the Iraq war is expected to criticise establishment figures beyond Tony Blair and his inner circle.

Among those who could be in focus are Jack Straw, the foreign secretary at the time of the invasion; Sir John Scarlett, chairman of the joint intelligence select committee; Sir Richard Dearlove, then head of MI6; Ms Short, then international development secretary, and Geoff Hoon, then defence secretary.

Meanwhile, Sir Stanley Burton, Lord Justice of Appeal between 2008 and 2012, said the risk of a judicial challenge was ''exaggerated'', as there was no appeal process by which the courts could rule on specific findings.