Tony Blair was delayed from leaving the House of Commons and Whitehall was closed for more than an hour yesterday when school pupils staged a demonstration against the prospect of war in Iraq.
The protest, which included a sit-in outside Downing Street, was part of a nationwide walk-out of lessons by thousands of teenagers. About 300 demonstrated in Birmingham, 500 in Sheffield and there were protests in Leeds and Liverpool.
In London, the protest included 1,500 pupils from Hampstead School, 100 from Acland Burghley School in Camden and 100 from Sidcup Girls School. A few were dragged away from Downing Street by police on foot and on horseback as they tried to climb the security gates at its entrance.
In a separate incident, anti-war protesters led by the campaigning comedian Mark Thomas dumped seven sacks of cow dung outside Labour Party headquarters in Westminster.
Police in Cambridge arrested two boys aged 16 and a girl aged 17 for alleged public order offences. John Steel, the headteacher of Prince Henry's Grammar School, in Otley, near Leeds, suspended two sixth formers for inciting other pupils to walk out. The Birmingham protest included Jacob Hunt Stewart, 14, son of Lord Hunt of King's Heath, a health minister.
In London, demonstrators blocked a section of Parliament Square, prompting Commons authorities to seal the main Carriage Gate entrance to Parliament. The protesters then moved to Downing Street.
Many had their faces painted and they chanted "We shall not be moved" and waved banners stating "Not in my name". Rosie Deveney, 16, from Hampstead School, said: "We have just as much right to protest as anyone else."
The pupils, some of them members of the Stop The War coalition, said they had arranged the protest by e-mail and leafleting.