The Chilcot Inquiry into the Iraq war has appointed one of the most renowned experts on international law as an adviser, in what is viewed as an indication that the Blair government's legal justification for the invasion is to come under serious scrutiny.
Dame Rosalyn Higgins, who was the most senior female judge in the world when she was the president of the International Court of Justice, will advise the panel on legal issues as well as the wider investigation.
The announcement of her appointment came after repeated assurances by the inquiry's chairman, Sir John Chilcot, that his team would not carry out a "whitewash". He has insisted the committee "will not shy away from making criticism. If we find that mistakes were made... We will say so."
Tony Blair will be called as a witness and he and other witnesses will be reminded to tell the truth.
The legal case for the war, presented by the then Attorney General, Lord Goldsmith, became hugely contentious. The vast majority of international legal opinion disputed his claim that UN resolutions justified Britain joining the US in the attack.
There was disquiet among the Government's own officials and the Foreign Office lawyer Elizabeth Wilmshurst resigned over the issue.
Such was the concern over the legal advice that the country's most senior officers, including Lord Boyce, the then Chief of the Defence Staff, and General Sir Mike Jackson, the then head of the Army, asked for urgent clarification from Lord Goldsmith after he had presented his legal opinion.
One senior official connected to the Chilcot Inquiry said there was "no reason" why Lord Goldsmith could not be called as a witness.
Last year, Lord Bingham, the former senior Law Lord, said that in his view, the legal justification provided by Lord Goldsmith was incorrect.
On Tuesday, the inquiry panel met families of those who had died in Iraq, during which a number of relatives stated they believed the war was illegal. Some declared that Mr Blair should be prosecuted for war crimes.
Lieutenant-Colonel Colin Mildinhall, whose 26-year-old son Lieutenant Tom Mildinhall was killed by a roadside bomb, said: "I believe this country has been badly let down and been lied to. I would like to see some accountability... The prime concern I have is over the legality of the war."
Deidre Gover, whose 30-year-old son Flight Lieutenant Kristian Gover died in Basra, said: "My son as an officer was prepared to die for his Queen and country in a just conflict. This was totally unjustified and wrong, and I think that's what the inquiry will prove."
The inquiry panel is going through thousands of government documents before holding its first public hearings later this year. According to Whitehall sources, these include documents relating to the legal advice sought by Lord Goldsmith and his correspondence with the cabinet before he gave the government the legal go-ahead.
The government has previously revealed that in March 2003, Lord Goldsmith twice put his legal advice in writing. The first document, dated 7 March and seen by only a handful of ministers and officials, was 13 pages long. It is reported to have argued that the case for war might not stand up in court. The second, circulated to the cabinet on 17 March and published as a parliamentary answer the same day, consisted of only 337 words in nine paragraphs. It declared unequivocally that the war was legal.
The inquiry has also appointed General Sir Roger Wheeler as military adviser to the panel. General Wheeler was not involved in the Iraq campaign.
Dame Rosalyn was appointed president of the International Court of Justice in 2006 and stepped down this year. During her tenure, the court determined that Serbia under Slobodan Milosevic was guilty of ethnic cleansing in the Balkans.