The long-awaited official inquiry report into Britain's bitterly contested invasion of Iraq will finally be published today amid calls for Tony Blair to be held to account for taking the country to war.

Thirteen years after British troops crossed into Iraq and seven years after the inquiry began work, Sir John Chilcot will deliver his verdict on the UK's most controversial military engagement of the post war era.

What is the Chilcot report?

It is the inquiry into the Iraq War.

It was set up in 2009 by then Prime Minister Gordon Brown to investigate the UK's involvement in Iraq.

It was tasked with examining almost a decade of decisions from 2001 to 2009.

This included the decision to go to war, whether British troops were adequately prepared, the military action, what planning there was for the aftermath and what lessons can be learned.

It soon became known as the Chilcot Inquiry after its chairman Sir John Chilcot, a retired civil servant.

When will the report be available?

The inquiry by Sir John Chilcot will deliver its report at 11am today.

Sir John will give a short statement to journalists in Westminster and the report will be published in full when he finishes. There are 12 volumes of it.

It'll be available free online but hard copies are so big they'll cost £767 each.

David Cameron will then give a statement in the House of Commons, followed by Jeremy Corbyn , at 12.30pm straight after Prime Minister's Questions.

What will be in it?

Sir John has said from the outset he would not rule on whether the invasion in 2003 was legal in terms of international law, pledging to provide a "full and insightful" account of the decision-making process.

Much of the focus will be on the section dealing with the decision to go to war.

The inquiry heard evidence that Mr Blair and President Bush reached an agreement "signed in blood" they would topple Iraq dictator Saddam Hussein when they met at the president's ranch in Crawford, Texas, a year before the invasion - a claim Mr Blair denied.

However issues covered by the report run far wider - from the diplomatic build-up to the invasion following the 9/11 attacks on the Twin Towers in 2001 through to the end of the UK occupation in 2009.

They include the intelligence on Saddam's supposed weapons of mass destruction - the original justification for military action - and the legal advice of attorney general Lord Goldsmith, who finally gave the green light just days before the invasion, having previously warned that further authorisation from the UN Security Council was needed.

It will also look at the equipment supplied to British troops, amid claims they were not given adequate protection, and the preparations for the occupation which saw Iraq descend into a bloody civil war in which tens of thousands - some estimates say hundreds of thousands - of civilians died.

When does it range from?

It starts with the summer of 2001 before the attacks on the World Trade Centre

It then moves to the war on Afghanistan, the build-up to military action in Iraq and the spring 2003 bombing on Baghdad followed by invasion.

It continues right up until when the inquiry was announced in July 2009 to capture the conflict's aftermath.

Will it be critical?

With some families of the British personnel killed and injured in the conflict already dismissing the report as a "whitewash", Sir John insisted they had not shied away from criticism where it was justified.

"I made very clear right at the start of the inquiry that if we came across decisions or behaviour which deserved criticism then we wouldn't shy away from making it," he said in an interview.

"And indeed, there have been more than a few instances where we are bound to do that. But we shall do it on a base of a rigorous analysis of the evidence that supports that finding."

Why has it taken so long?

It has just seven years - five years longer than originally expected.

Sir John acknowledged the frustration at the time taken to complete the report but said they had faced a "huge task" in sifting through the tens of thousands of official documents as well as taking oral evidence from dozens of politicians, generals, diplomats and spies.

He had originally hoped it would be ready within two years of starting work in 2009, but it has since been hit by a series of delays.

The most serious has been bitter wrangling between the inquiry and the Cabinet Office over the de-classification of hundreds of official documents - most notably communications between Mr Blair and US president George Bush.

In May 2014 it was finally announced an agreement had been reached between Sir John and Cabinet Secretary Sir Jeremy Heywood that "gists or quotes" from the correspondence could be published, although Mr Bush's views would not be reflected.

That was followed by a further period of delay while the inquiry carried out the so-called Maxwellisation process - allowing individuals facing criticism the chance to respond before the report was finalised.

Will anyone face prosecution?

The prosecutor at the International Criminal Court, Fatou Bensouda, has already made clear that charges cannot be brought in relation to the decision to go to war as the court has no jurisdiction over the "crime of aggression".

However General Sir Michael Rose, who commanded British troops in Bosnia in the 1990s and has been advising the families of some of the British dead and injured, said they were preparing to launch a civil action against Mr Blair.

"He has a personal responsibility as leader of this country to properly assess the intelligence and information that he is using to justify going to war," he told BBC Radio 4's The World at One.

"The consequences of that war have been utterly catastrophic. The families want to see justice and if it proves as a result of reading the report that there was dereliction of duty, malfeasance in public office, intelligence was negligently handled, then they will take action."

Who is Sir John Chilcot?

Sir John was a career diplomat before his appointment as chairman of the Iraq Inquiry.

With his experience on a number of similar panels, Sir John was widely considered to be a safe pair of hands to lead the review into the circumstances surrounding the invasion of Iraq.

But he has also come under criticism for the time taken to complete the Iraq Inquiry.

His questioning style was also criticised by Philippe Sands QC for being, at times, "surprising" and "rather pathetic".

However, Sir John has won praise for advocating openness within the inquiry after setting out that he wanted to hold hearings in public "wherever possible" in his opening speech.

Sir John was the top civil servant at the Northern Ireland Office during the height of the troubles and helped prime minister John Major negotiate with the Irish Government.

He retired from the civil service in 1997 and went on to become staff councillor to the Intelligence Services and chaired the Building and Civil Engineering Group before heading up the inquiry.

Sir John also held the post of chairman of the advisory committee at the Centre for Contemporary British History.

He is president of the independent think tank the Police Foundation; a trustee of the Police Rehabilitation Trust; and a member of the Awards Council of the Royal Anniversary Trust.

Have there been any other investigations?

There have already been four separate inquiries into aspects of the Iraq conflict.

In 2003, the Commons Foreign Affairs Committee and the joint Parliamentary Intelligence and Security Committee both looked into the intelligence used to justify the war.

The Hutton inquiry, in January 2004, examined the circumstances surrounding the death of scientist and weapons adviser Dr David Kelly.

And the Butler inquiry in July 2004, looked at the intelligence which was used to justify the war.

Here are some of the key numbers relating to the inquiry:

  • SEVEN Years since the Chilcot Inquiry was launched, although the report of the inquiry's findings was originally intended to be ready for publication by the end of 2010.
  • 2,578 days between June 15, 2009, when the inquiry was announced by then-Prime Minister Gordon Brown, and July 6 2016, when the report will finally be seen by members of the public.
  • THREE foreign secretaries to have been in the post since the inquiry was launched - David Miliband under Mr Brown, and William Hague and Philip Hammond under David Cameron.
  •  2.6 million words estimated to be included in the report.
  • 10 million pounds, the cost of the inquiry, according to recent estimates.
  • 179 UK fatalities during the Iraq war, including 47 who died from roadside bombs and IEDs.
  • TWO times Tony Blair, the Prime Minister at the time of the invasion, was called to give live evidence before the inquiry.
  • 12  volumes of the report.
  • 767 pounds, the cost of ordering a copy of the report. Families of those killed in the war will have the costs waived having originally been told they would have to pay for it.
  • 150,000 -government documents believed to have been scrutinised for the report.