Police breached campaigners' right to protest peacefully when they stopped two coaches going to an anti-war rally, the Law Lords have been told.
The hearing is expected to last for three days
The demonstrators were prevented from attending the rally at RAF Fairford in Gloucs., days after the coalition forces launched the Iraq war in 2003.
Ben Emmerson QC, said it was a right for citizens to demonstrate on matters of public interest.
Gloucestershire police will defend their actions in the three-day hearing.
Police lawyers will argue they were upholding demonstrators' human rights by protecting their lives, which would have been put at risk if they had broken into the base.
Mr Emmerson said it was the police's responsibility to maintain order "in a manner which respects the rights of those who wish to demonstrate peacefully".
Police who authorised the coaches to be stopped and passengers searched while detained - and then forced back to London under escort - had breached that right, he said.
The coaches were stopped by police outside Lechlade near Fairford.
About 90 of those detained formed the Fairford Coach Action to try to seek judicial condemnation.
The group says that although the High Court and Court of Appeal ruled the police acted unlawfully in detaining them, it was ruled that the police did not violate their right to freedom of movement and lawful assembly.
The Law Lords are being asked to overturn this ruling.
Mr Emmerson said the police had behaved in a way that was "premature and indiscriminate".
He said in order for the police action to be lawful, they had to show there was an imminent danger of public order offences.
The action was allegedly premature because 120 people who wished to take part in the demonstration were turned away when the police knew there was no imminent danger of disorder.
Mr Emmerson said it was discriminatory because the police took action against a large number of people because of the "perceived intention" of some individuals.