The event in Berkshire was organised by the Coalition Against the Criminal Justice Act as a protest against the new offence of aggravated trespass contained in the Act, which became law last November.
Steve Platt, editor of the New Statesman and Society magazine and organiser of the march, was among those held by police. As he was led away he said that he was arrested for obstruction adding: "I have never seen an arrest for something like this. It's ridiculous."
The original plan had been to march illegally across Prince Albert's Walk, an area of land in the castle grounds which has been closed to the public for 150 years and governs access to a towpath along the Thames. But the Crown Estates agreed to open the land to the public for the duration of the march, a decision apparently taken with the agreement of the Royal Family.
Dixie Dean, from the Coalition Against the Criminal Justice Act, said: "We've won a victory. We're the first people to have been allowed on Prince Albert's Walk for 150 years. Now we want access for 365 days a year, not just one."
Paul Jacques, of Thames Valley Police, said: "Given the nature of the event, it was necessary to use a substantial amount of officers, about 400, all of whom were used to keep the peace."
The atmosphere grew tense as police reinforcements arrived and there were several clashes between officers and marchers. At one stage about 60 people climbed a fence, ran on to the Crown Estate land and lay down in front of a line of mounted police, preventing them from advancing on the protesters.
The biggest clashes came at the end of the march, when protesters tried to rush some gates which were being guarded by police. Four lines of mounted officers and two lines of foot officers charged the marchers, pushing them back along the road. Police said there were "disruptive elements" in the crowd. "Missiles were thrown at officers and regrettably some arrests were necessary."
But despite the clashes, both organisers and police claimed to have achieved their aims. Ms Dean called the event a "success, a victory", while Thames Valley Police said their policy of "achieving a balance" had ensured that "the event was largely peaceful."Reuse content