- guardian.co.uk, Friday 29 January 2010 08.53 GMT
The former prime minister avoided hundreds of demonstrators by entering the inquiry venue through a cordoned-off rear entrance at about 7.30am, two hours before the hearing was due to begin.
Demonstrators accused him of cowardice for "sneaking" into the building. The chairman of the anti-war group, Andrew Murray, said: "This cowardly and deceitful entrance is typical of how the former prime minister sold the war to the country – behind the backs of the public."
Sir John Chilcot and the four other members of the inquiry will question the former prime minister for six hours today at the QE2 centre in London, where police have mounted a large security operation.
Blair has always defended his decision to send British troops to join the American-led invasion in 2003 and today he is expected to strongly assert that he acted in good faith and that the war brought benefits to the people of Iraq.
But he is likely to face tough questioning about the events leading up to invasion, and in particular about the allegation that he was giving private assurances to the US president, George Bush, about Britain's willingness to go to war that contradicted what he was telling parliament and the public in the months leading up to the war about no decisions having been taken.
Blair resisted calls for a public inquiry into Iraq while he was in office and some Labour figures believe that the party's electoral prospects could be damaged by the evidence that has been emerging since Chilcot started taking evidence in November last year.
Gordon Brown originally wanted the inquiry to sit in private when he set it up, but Chilcot decided that almost all evidence should be heard in public.
The inquiry held a ballot for today's hearing, which will start at 9.30am, and more than 3,000 people applied. There are 60 seats in the room where Blair is giving evidence, and another 700 seats in the QE2 centre where people can watch the proceedings on a screen, but all the places have been allocated, and the inquiry has asked anyone without a ticket to stay away.
The inquiry has heard that Blair started preparing for war in 2002, and he will be asked about the private assurances he gave to Bush, particularly at a meeting they held at Crawford in Texas in April 2002 and in a series of private letters he sent to the US president later that year.
Sir Christopher Meyer, the US ambassador to Washington at the time, told the inquiry last year that he still did not know "what degree of convergence was, if you like, signed in blood, at the Crawford ranch".
Blair justified the decision to go to war on the grounds that he wanted to disarm Iraq and force it to comply with the conditions imposed by UN resolutions. But Lord Turnbull, the cabinet secretary at the time of the war, told the inquiry that he thought Blair was originally a believer in "regime change" and he urged the inquiry to question Blair about this closely.
Turnbull said he was surprised by the interview Blair gave to Fern Britton last year in which he said that he would still have thought it right to remove Saddam Hussein, even if he had known Iraq had no weapons of mass destruction.
Turnbull said the inquiry should question Blair about the comment on the grounds that it appeared to contradict what he said about disarmament being the reason for the war.
Blair will also be questioned about the dossier published in September 2002 about Iraq's weapons of mass destruction.
Chilcot himself has suggested that it was wrong for Blair to say in the foreword to the document that the intelligence about Iraq's WMD was "beyond doubt", and other members of the inquiry have suggested that there was no evidence to support Blair's claim that the WMD threat from Iraq was "growing".
The inquiry will want to know why Blair did not allow the military to start buying the equipment it needed for war at an early stage. Geoff Hoon, defence secretary at the time, told the inquiry that Blair did not want this work to begin too soon because it would undermine his attempts to get an agreement at the UN.
Blair will also be asked about the planning for postwar Iraq. The inquiry has heard complaints from many witnesses about the fact that Britain and the US did not prepare properly for the aftermath and, although Blair raised concerns about this with Bush, the evidence suggests that his warnings were ignored.