As hundreds committed the offence of putting ink to cardboard, police moved in

Nurses, doctors, retired people and architects among more than 400 protesters arrested as terrorism suspects.

- John Simpson reports

One by one the police took them away. Some were carried, some walked. In every case, officers read them their rights, saying the words: "I am arresting you under the Terrorism Act.

Many among the silent protesters in Parliament Square yesterday had to be asked if they were mobile enough to make the short walk to the police van.

At 1pm, marker pens came out. Many people had already begun writing the offending sentence: "I support Palestine Action." The chimes of Big Ben rang out as hundreds committed the offence: putting ink to cardboard.

Soon after, teams of officers from the Metropolitan police, who eschewed riot gear, began to approach the protesters, all seated with their backs to the Palace of Westminster.

Some 600 to 700 protesters sat on the lawn, largely in silence. One by one the arrests began. More than 400 protesters were arrested by last night.

One young officer showed the offending placard to the man he was arresting, saying: "You were holding a sign saying 'I oppose genocide, I support Palestine Action.'

"Now Palestine Action is a proscribed group under the Terrorism Act 2000, which means you have committed an offence under section 12 of that legislation, which is why I am arresting you today."

The man said simply: "I am not a terrorist" as an angry voice from the crowd yelled: "You are arresting the conscience of this country."

Among the arrests were the environmentalist Sir Jonathon Porritt and former Guantanamo Bay prisoner Moazzam Begg, who runs the advocacy group Cage, whose stated aim is challenging "war on terror-driven" state oppression.

John Woodcock, who as an adviser to the last government first called for Palestine Action to be banned, said it was an organised attempt to "subvert the law by overwhelming the criminal justice system". "It can't be allowed to succeed," he added.