Peace protesters and civil rights groups celebrated an "enormous victory for free speech" after the House of Lords condemned the police for preventing a demonstration outside an airbase used in the Iraq war.
Hours before American B-52 bombers took off from RAF Fairford in Gloucestershire in March 2003, 120 opponents of the invasion were travelling from London in three coaches to protest outside its gates.
A few miles away they were stopped by police who confiscated a Frisbee and a bag of toy soldiers during a two-hour search. Their coaches were then sealed and escorted in convoy, without even allowing lavatory stops, back to London.
The High Court and Court of Appeal have already said police acted unlawfully. They won a further landmark ruling yesterday when the Law Lords unanimously concluded that police violated their right to lawful assembly and to freedom of expression, which was "an essential foundation of democratic society".
Lord Bingham of Cornhill, giving the lead judgment, said the case raised "important questions on the right of the private citizen to demonstrate against government policy and the powers of the police to curtail exercise of that right".
He said the police action, designed to thwart a future breach of the peace, was "wholly disproportionate" under the European Convention on Human Rights.
Shami Chakrabarti, the director of Liberty, said: "This is an enormous victory for free speech in a time when this principle is under considerable threat. Once again, democracy was in trouble and the Law Lords came to its rescue."
Jane Laporte, the passenger in whose name the case was brought, said: "The Lords have confirmed that freedom to protest is something that should be treasured in this country and police don't have the right to take it away."
John Halford, a human rights specialist at Bindman and Partners, which represented the campaigners, said that the judgement was "a wake-up call for democracy".
Gloucestershire Police said that it was disappointed by the judgment and defended its actions.
"Policing in scenarios such as those faced at Fairford is difficult and complex, with competing rights and responsibilities having to be assessed and acted upon in real time by operational commanders," it said.
It claimed that intelligence had suggested a potential for disorder after US B-52 bombers at the base were targeted by anti-war campaigners during earlier demonstrations.
It was against "this highly charged background" that the coaches were turned back, police said.