Blair to make second appearance at inquiry, a year after he first gave evidence, in light of revelations about advice he received on the legality of the war

Tony Blair, summoned back to the inquiry into the Iraq invasion in light of damaging and conflicting evidence revealed since he answered questions a year ago, is to appear before Sir John Chilcot on 21 January, it has been revealed.

A ballot has been held for 60 seats, with a third reserved for family members who lost loved ones in Iraq, the inquiry has announced. All the people who were successful in the ballot will be notified in the next few days, it said.

The former prime minister will attend in light of evidence about the legality of the invasion, and assurances he gave George Bush.

The inquiry is believed to be concerned about the revelation in documents released in June showing that the day before he privately assured Bush he would back US-led military action, Blair was warned by Lord Goldsmith, then attorney general, that an invasion of Iraq would be illegal.

Documents reveal how Goldsmith repeatedly warned Blair of the consequences of invading Iraq without fresh UN authority.

A note from Goldsmith to Blair, marked secret and dated 30 January 2003, stated: "I thought you might wish to know where I stand on the question of whether a further decision of the [UN] security council is legally required in order to authorise the use of force against Iraq."

Goldsmith warned Blair that "the correct legal interpretation of resolution 1441 [the last security council decision on Iraq] is that it does not authorise the use of force without a further determination by the security council". He concluded: "My view remains that a further [UN] decision is required."

The document contains a handwritten note, by David Manning, Blair's chief foreign policy adviser, which warned: "Clear advice from attorney on need for further resolution."

An apparently frustrated Blair scrawled in the margin: "I just don't understand this." An aide added: "Specifically said we did not need further advice [on] this matter."

The following day Blair flew to Washington to see Bush. Manning records the president telling Blair that military action would be taken with or without a second security council resolution, and bombing would start mid-March 2003.

The minute records Blair's reaction: "The prime minister said he was solidly with the president."

By 7 March, 2003, Goldsmith had told Blair that a new UN resolution might not be needed after all, though war without one would risk Britain's indictment before an international court.

On 17 March, Goldsmith, published a short note saying an invasion was lawful.

Lord Boyce, then head of the armed forces, Jack Straw, foreign secretary at the time, and three successive cabinet secretaries at the heart of the Whitehall machine will also be recalled.

The Chilcot inquiry has heard that Blair told Boyce, who was worried about the concerns expressed earlier by Goldsmith, that it was his "unequivocal" view that an invasion of Iraq would be lawful.

Goldsmith has been asked to supply the inquiry with further written evidence.

Lindsey German, convener of the Stop The War Coalition, said: "Blair will be met with demonstrations and protests at the Chilcot inquiry. Military families, former soldiers, peace campaigners, students and trade unionists will all be there.

"When two million marched in February 2003 we knew Blair was lying, we knew that the war was illegal. It seems so too did some at the highest levels of government.

"Blair should not be allowed to get away with lying again. We are determined to hold him to account and believe he should be indicted for war crimes over his wilfull determination to back George Bush and take Britain into this war."