A still image from video shows former British Prime Minister Tony Blair (BACK TO CAMERA) speaking at an inquiry into Britain's role in the Iraq War, at the Queen Elizabeth II Conference Centre, in central London January 21, 2011.[Photo/Agencies]

LONDON - The chairman of a long-running British public inquiry into the Iraq War said on Thursday he expected to complete his report next April and publish it in either June or July 2016.

The inquiry aims to shed light on every aspect of Britain's involvement with Iraq from 2001 to 2009, from the build-up to the US-led invasion in 2003 to the withdrawal of combat troops, and to identify lessons that can be learned.

The Iraq War, and in particular the role of former Labour Prime Minister Tony Blair in leading the nation into it, are still live political issues in Britain and the inquiry has come under repeated criticism from lawmakers and relatives of those killed over how long it has taken.

"My colleagues and I estimate that we will be able to complete the text of our report in the week commencing 18 April 2016. At that point, national security checking of its contents ... can begin," John Chilcot said in a letter to Prime Minister David Cameron published on the inquiry's website.

Chilcot said due to the length of the report - more than 2 million words in total - it would then take many weeks to prepare for printing, making publication in June or July most likely.

British Prime Minister David Cameron said he was disappointed that the inquiry did not intend to publish its findings until mid-2016.

"Whilst it is welcome of course that there is now a clear end in sight for your inquiry, I am disappointed - and I know the families of those who served in Iraq will also be disappointed - that you do not believe it will be possible logistically to publish your report until early summer," Cameron said in a letter in to the head of the inquiry John Chilcot.

"I recognise that you have a significant task, but would welcome any further steps you can take to expediate the final stages of the inquiry," he said in the letter, which was released by his office.

Publication has been held up by so-called "Maxwellisation", a confidential process in which people who are to be criticised in the inquiry report are given advance copies of the draft so that they have a chance to defend themselves.

On Sunday, US network CNN aired an interview with Blair in which he apologised for what he described as mistakes in planning and intelligence before the war, with media accusing him of trying to pre-empt criticism in the report.