During 37 years in public administration, Butler rose to become perhaps the ultimate establishment insider, eventually serving as head of the civil service under three different prime ministers.

The last of these was current premier Tony Blair, whose government could be dealt a severe blow should Butler report on Wednesday that it relied upon -- or worse, encouraged -- misleading information about Iraq's weapons of mass destruction.

When he was appointed to lead the inquiry in February, Butler, now 66, was dismissed by some critics as being far too much of an unctuous mandarin to criticise ministers with any independence.

His background undoubtedly offers evidence for such a view.

Educated at Harrow School, a favourite of the rich and well-connected, and then Oxford University, Butler joined the Treasury as a junior civil servant in 1961.

Rising steadily through the ranks, he became Cabinet Secretary -- head of the entire domestic-based civil service -- in 1988, a post he kept until retirement a decade later.

Butler's judgement was called into question during the 1990s when he investigated a pair of Conservative lawmakers accused of corrupt practices, Neil Hamilton and Jonathan Aitken.

Butler found little wrong in their conduct -- only to be publicly proved very wrong when Hamilton resigned from the government for accepting money to ask parliamentary questions while Aitken was jailed for perjury.

Butler also found himself quite literally in the firing line on a couple of occasions.

In 1984 he narrowly escaped being killed when a bomb planted by Northern Ireland paramilitary group the IRA destroyed part of a hotel in the coastal resort of Brighton where then-prime minister Margaret Thatcher and her ministers were staying.

Seven years later Butler flung himself to the floor alongside Thatcher's successor, John Major, as IRA-fired mortar rounds landed in the garden of Downing Street.

The incident is occasionally remembered as the only time contemporaries saw Butler behave with anything other than complete dignity.

After his retirement, the grey-haired Butler, married for 42 years and with three children, was made a peer and became head of one of Oxford University's colleges.

Despite his pedigree, Butler might surprise people who expect such a figure to side with the government, said Paul Kelly, a lecturer in politics at the London School of Economics.

"He's definitely an establishment figure but he's a very sensible and cautious, small "c" conservative figure, who will be aware of the longer-term reputation of government," Kelly told AFP when Butler was appointed.

"His concern, I think, in his position in the establishment is to look at the lasting trust in institutions.

"He's going to be very concerned about the standing of the intelligence services, the civil service, the reputation of government itself -- not just this particular government."

WAR.WIRE