UK's Blair faces "pivotal day" at Iraq War inquiry

British Middle East envoy Tony Blair speaks at the Global Competitiveness Conference, an annual gathering of Saudi and world businessmen, in Riyadh January 25, 2010.

LONDON (Reuters) - Former British prime minister Tony Blair makes a much-anticipated appearance before an inquiry into the Iraq War on Friday, his personal reputation as well as that of the Labour government at stake.

The decision to send 45,000 British troops to invade Iraq in 2003 was the most controversial of Blair's 10-year premiership, provoking huge protests, divisions within his Labour Party and accusations he had deceived the public over his reasons for war.

Seven years after the U.S.-led invasion to topple Saddam Hussein, and almost three years after Blair handed over to Gordon Brown, the issue still provokes anger.

Families of some of the 179 soldiers killed in Iraq will

join an anti-war demonstration outside the building calling for Blair to be considered a war criminal.

Some Labour leaders fear the inquiry, and especially Blair's appearance, will reignite strong feelings on the issue among voters, denting support for a party already trailing the Conservatives in polls in the run-up to an election due by June.

"It's a pivotal day for him, for the British public and for Britain's moral authority in the world," said Anthony Seldon, a political commentator and biographer of Blair.

"This is an enormous day and it goes way beyond him and his own reputation."

The inquiry is likely to focus on the public justification the government gave for war, notably the "dodgy dossier" of September 2002.

Blair said in the dossier that intelligence had "established beyond doubt" that Iraqi ruler Saddam Hussein possessed weapons of mass destruction (WMD). No such weapons were ever found.

The inquiry has already heard from senior civil servants who said intelligence in the days before the March 20, 2003 invasion indicated that Saddam's WMD had been dismantled.

It will also examine the war's legitimacy and at what stage Blair promised U.S. President George W. Bush that Britain would support military action against Iraq.

Witnesses have suggested Blair gave that assurance in 2002 although then Attorney General Peter Goldsmith, the government's top lawyer who eventually gave the invasion the green light, had warned him that using force for regime change would be illegal.

ATTORNEY CHANGED HIS MIND

Indeed Goldsmith told the inquiry he originally believed the United Nations had to approve the use of force and only changed his mind a month before the invasion.

The two top foreign ministry lawyers said they had told the government the war would be unlawful.

Commentators say Blair's evidence is unlikely to produce any startling revelations. Members of the inquiry, set up by Brown last year to learn lessons from the war and the third major probe into the conflict, have stressed that it is not a trial.

Critics also say the five-person team has been too soft on witnesses and failed to ask probing questions.

Blair himself has taken some of the sting out of the hearing by telling an interviewer in December that he believed it was right to oust Saddam even though no WMD were found.

Despite this, the inquiry has continued to make frontpage news and TV news channels have carried extensive live coverage.

Robert Worcester, founder of polling group MORI, said the war remained an election issue and could damage Brown -- finance minister at the time -- if Blair tied him into the decision to back the invasion.

"Enough people are paying attention to what's going on in this inquiry to make a perceptible difference and the issue is sufficiently strong in a relatively small but important segment of the public's mind to have an impact," he told Reuters.

Peter Kellner, president of polling firm YouGov, said Blair's appearance was unlikely to make great waves unless he said something dramatic. "On the Iraq issue, the people who feel strongly about it made up their mind years ago," he said.

For Blair, now Middle East envoy for the Quartet of powers, Friday's hearing could affect both how history will view him and his future career as a speaker.

"I think he has a chance to make an enormous difference now to the way his premiership is seen," Seldon said.

(Editing by Tim Pearce)