Sleeping bags cluttered the pavement outside a London courtroom on Thursday as bleary-eyed Britons and jeering demonstrators lined up to watch Prime Minister Tony Blair face a tough day in the witness stand.

Hoping to gain admission to the Royal Courts of Justice, dozens of people had been waiting since the previous afternoon, some bringing tents to keep out the chill until Blair's arrival.

Blair began testifying at around 10:30 am (0930 GMT) before a judicial inquiry into the apparent suicide of weapons expert David Kelly, the former arms inspector at the centre of allegations that Britain exaggerated its case for war against Iraq.

By 9:30 am several hundred people, both members of the public and media, had massed outside the building, with a rowdy demonstration gathering momentum at the main entrance in London's West End.

"I came to see him hang himself," said Faye Davies, a press officer in her thirties, who said she felt let down by Blair's Labour government.

Demonstrators held up posters of Blair, of Foreign Secretary Jack Straw and Defence Secretary Geoff Hoon, scrawled with slogans such as "Blair and Bush wanted for war crimes," or "Bliar", an increasingly common pun on the prime minister's name.

Thursday's hearing took place amid tight security, with a police helicopter circling overhead, and officers posted outside the courtrooms with dogs trained to detect explosives.

Blair was to be questioned over claims his office "sexed up" a dossier arguing the case for war on Iraq and over his role in the outing of Kelly as the source of the claims, carried in a BBC report.

One protestor carried a placard around his neck reading: "Trust me, I'm Tony."

Alex Holmes, an 18-year-old freshman history student at Oxford, southeast England, arrived at nightfall on Wednesday and took up first place in the queue.

"I had no idea what time I should get here because it's my first day at the inquiry, but I knew I wanted to be in the first 10," he said.