Alastair Campbell faces the moment of truth

Today could see the Chilcot inquiry's most explosive encounter yet. Michael Savage rehearses the arguments

Alastair Campbell faces potentially explosive questioning today over his role in overstating the reliability of intelligence on Saddam Hussein's weaponry, as he becomes the first major political figure to appear before the Iraq inquiry.

Tony Blair's former Downing Street director of communications is expected to be quizzed over a key claim that it was "beyond doubt" that Saddam had weapons of mass destruction (WMD), made in a dossier published in September 2002 setting out the Government's case for war.

The assertion appeared in a foreword to the document, which appeared under the name of Mr Blair. However, Mr Campbell has already admitted that he was responsible for drafting it.

Sir John Chilcot, the chairman of the Iraq inquiry, has shown a close interest in the claim. Several senior Whitehall figures have told the inquiry that the assertion was made despite the fact that the Prime Minister was warned that intelligence on Saddam's weaponry should be treated with caution.

Critics of Mr Campbell's involvement in building the Government's case for war in Iraq are expecting the former spin doctor to go on the offensive today, a tactic he has deployed in the past. In 2003, he used his appearance before the House of Commons foreign affairs committee to demand an apology from the BBC for its suggestion he exaggerated claims that Saddam had WMD that could be used within 45 minutes.

Norman Baker, the Liberal Democrat MP who has written a book on the dossier, said key questions on Mr Campbell's role over the dossier must be asked by the committee. "They [Downing Street] replaced all the question marks with exclamation marks," he said. "The whole process of forming the dossier was to make a political case for war."

Senior political figures who formed part of Mr Blair's top team will next week follow Mr Campbell in giving evidence to the inquiry. The former Defence Secretary, Geoff Hoon, will be called next Tuesday, and the Justice Secretary, Jack Straw, next Thursday. Mr Straw will likely be quizzed about a private letter he sent to Mr Blair shortly before the invasion, in which he suggested that the Government should pursue policies short of military action.

David Cameron yesterday appeared to back Mr Blair's claim that military action was needed without the WMD claim. "I voted for it. I haven't gone back on that decision," he said.

Here we lay out six key questions for Alastair Campbell.

Why did you have so much influence over the September dossier?

Controversy has always surrounded his role in formulating the September 2002 dossier on Iraq, which claimed that Saddam Hussein had weapons of mass destruction that could be launched within 45 minutes. It is already known that Mr Campbell was at editing meetings for the document and that he suggested 11 separate changes to the draft dossier. Critics maintain that Mr Campbell had too much power over the formation of the dossier, which was overseen – in theory – by the intelligence chief, Sir John Scarlett.

Did you come up with the phrase that Saddam's ownership of WMD was "beyond doubt"? If not, who did?

Sir John Scarlett has already conceded to the inquiry that it may have been more appropriate if the Prime Minister's foreword, that said Saddam's ownership of WMD was "beyond doubt", had not been included. Whitehall figures have suggested that the reliability of the intelligence which formed the basis of the claim was overstated. Mr Campbell drafted the foreword.

Were crucial claims about Iraq's theoretical nuclear capabilities changed to fit statements made by President George Bush?

New accusations have emerged that Mr Campbell asked that one of the claims in the dossier, about Iraq's potential to build nuclear weapons, be altered to match claims made by the Bush administration. Other officials have told the inquiry that a claim that aluminium tubes spotted in Iraq could be used in a nuclear programme was included after US vice president Dick Cheney mentioned them during a television interview.

Why did you pressure senior figures to be more optimistic over war plans?

The former head of Britain's armed forces revealed that he was told by Mr Campbell to be more positive about the Government's plans to invade Iraq. Admiral Lord Boyce raised concerns about keeping war plans a secret from the public, preventing him from ordering crucial equipment. He said Mr Campbell asked him to give a "half-full rather than half-empty assessment" during briefings at No 10. Other senior figures were targeted after raising concerns. Lord Goldsmith, the former Attorney-General, is said to have been banned from speaking out by Mr Blair and his closest advisers after informing the Prime Minster that an invasion of Iraq may not be legal.

Why were warnings on delaying the invasion ignored? Why wasn't action taken to improve post-war planning?

Major General Tim Cross, the most senior military figure appointed to help plan the aftermath, returned to London two days before the invasion and told Mr Campbell that reconstruction planning was far from complete. Mr Campbell then brought the Prime Minister to meet Maj Gen Cross, and was present when Maj Gen Cross informed Mr Blair that military action should be delayed.

What concerns did you have about the image of the invasion?

There has been mounting evidence at the inquiry that No 10 obsessed over the media image of the Iraq campaign as one of the most pressing priorities. During his meeting with Maj Gen Cross, Mr Campbell pledged to send reinforcements to improve the media operation of the main post-war planning unit. Sir Jeremy Greenstock, who was Britain's special representative in Iraq, said Mr Blair ordered him to make improving the media image of the campaign a main priority, alongside boosting security.