TONY Blair faces fresh questions about his decision to take Britain to war with Iraq when he makes his second appearance before the Chilcot Inquiry into the war today.

The former prime minister and MP for Sedgefield has been recalled to explain gaps in his earlier evidence and apparent discrepancies between his account and official documents and other witnesses testimony.

He is expected to be grilled about what promises he made to former US president George Bush and his attitude to the advice about the legality of the war he received from former attorney general Lord Goldsmith.

The inquiry panel will ask Mr Blair about the secret messages he sent to Mr Bush in the build-up to the March 2003 invasion of Iraq.

It emerged this week that the head of the Civil Service, Cabinet Secretary Sir Gus O'Donnell, has refused requests for extracts from the notes to be released.

Inquiry chairman Sir John Chilcot said he was disappointed by the decision, which he pointed out flew in the face of revelations about the contents of the documents in Mr Blair and Mr Bush's recent memoirs.

Sir John said the question of when and how the former prime minister made commitments to the US about Britain's involvement in military action against Iraq was central to the inquirys considerations.

Ex-Downing Street communications director Alastair Campbell told the inquiry last year that Mr Blair's secret messages assured Mr Bush that Britain would be there if it came to military action.

Fresh evidence emerged this week of Lord Goldsmiths misgivings about how his legal advice was being used in the period before the war.

The former attorney general revealed he was uncomfortable about Mr Blair's public comments that Britain could attack Iraq without further United Nations' backing when he was receiving clear legal advice to the contrary.

Lord Goldsmith told the prime minister on January 14 2003 that there was no room for rejecting a veto of a resolution explicitly authorising military action by a permanent UN Security Council member on the grounds that it was unreasonable.

But the next day Mr Blair told the Commons it was necessary to be able to say that Britain would still act if an unreasonable veto was put down.

And on February 6 he reiterated to the BBC's Newsnight programme that he would consider action if a Security Council member unreasonably vetoed a further resolution.

It was not until March 7 2003 - less than a fortnight before the invasion - that Lord Goldsmith presented Mr Blair with formal legal advice that a reasonable case could be made for launching an attack without extra UN backing.

Mr Blair is also expected to be asked about a memo, dated January 30 2003, in which Lord Goldsmith advised him that UN Security Council Resolution 1441 did not authorise the use of military force against Iraq on its own.

A scribbled note next to this sentence, apparently in the former prime minister's handwriting, says: "I just don't understand this."

The next day Mr Blair reportedly told Mr Bush at the White House that he was solidly with him after the US president said the bombing of Iraq was planned to begin in mid-March.

Critics have suggested the attorney general was heavily leaned on by Downing Street to agree that the invasion would be lawful.

Mr Blair could also be questioned about evidence that MI5 said in March 2002 that Saddam Hussein's capacity to mount terrorist attacks against the UK was limited.

The security agency added that it had yet to see convincing intelligence of useful co-operation between Iraq and al Qaida about sharing chemical and biological weapons.

Appearing before the inquiry in July, former MI5 head Baroness Manningham-Buller dismissed Mr Blair's argument that Britain and the US needed to take action against Saddam Hussein after the 9/11 attacks to prevent his supposed weapons of mass destruction being obtained by terrorists.

"It's a hypothetical theory. It certainly wasnt of concern in either the short term or medium term to my colleagues and myself," she said.

Mr Blair mounted a vigorous defence of the invasion of Iraq when he appeared before the inquiry on January 29 last year, insisting he had no regrets over removing Saddam and would do the same again.

But opponents of the war and families of the 179 British troops who died in the conflict condemned his appearance, saying he evaded the panels questions and refused to admit his mistakes.

As Mr Blair left the hearing room after giving evidence for six hours, one audience member heckled: "You are a liar," and another added: "And a murderer."

In his memoirs, A Journey, published in September, the former prime minister said he was angry at the way he was asked whether he had any regrets about going to war.

He wrote that the Chilcot Inquiry was supposed to be about learning lessons, but had inevitably turned into a trial of judgment and even good faith.

Among those watching Mr Blair give evidence in the inquiry chamber today will be Reg Keys, whose son, Lance Corporal Tom Keys, 20, from Llanuwchllyn, near Bala in North Wales, was one of six members of the Royal Military Police killed by a mob in southern Iraq in June 2003.

He said: "I'm not even in the room at the moment and I feel emotional about it as Blair is the man responsible for the death of my son.

"Had he been killed by weapons of mass destruction - had Iraq possessed them - I would accept that. But I will not accept that a prime minister in the 21st century can mislead Parliament and get away with it."

Mr Keys, an outspoken critic of the war who stood against Mr Blair in the 2005 general election, said he still held the former prime minister responsible for his son's death.

He was scathing about Mr Blair's attitude to the bereaved relatives in the audience when he appeared last time.

He said: "Sir John gave him the opportunity when he asked 'Do you have any regrets?' All he had to do was half turn around to where the families were sitting and say 'I do regret the death toll'.

"The unfortunate thing is he will be given the questions before he gets there, and of course he can get his team of silky wordsmiths to come up with responses.

"Last time he was able to dodge the questions. At times last time I was screaming silently inside 'Bring him back to that question'. I only wish he was under oath."

The Metropolitan Police ran up a bill of £273,000 to protect Mr Blair when he first appeared before the inquiry.

Anti-war campaigners will again stage demonstrations outside the Queen Elizabeth II Conference Centre in Westminster, central London, when he gives evidence over four-and-a-half hours today.