Peace campaigners are to appeal against a High Court ruling that the police acted lawfully in blocking a coach load of people attending an anti-war demo.
The buses did not stop during the journey back to London
More than 120 passengers were searched, detained and returned to London after attempting to reach an anti-Iraq war demo at RAF Fairford.
The court recently ruled it was not unlawful for police to turn the passengers away from the airfield.
Protesters say it means anybody could be turned away at the whim of police.
Helen Wickham, who was stopped from attending the rally at the Gloucestershire base in July 2003, said: "To be sure of reaching a demonstration, I would have to be psychic.
"I would need to know what's going on in the mind of a senior police officer."
Lawyers for the group will argue in the appeal court that the police actions in turning them away were contrary to the common law.
The case is being supported by Amnesty International and Liberty.