Lawyers for half the 120 passengers, stopped from protesting last March, accused Gloucestershire Police of acting unlawfully.
Lord Justice May and Mr Justice Harrison, sitting in London, ruled that the protesters' detention and forced return could not be justified under the European Convention on Human Rights.
The protesters were on their way to join a demonstration against the war in Iraq when they were detained.
Police lawyers had said the officers were not only entitled to take the action they did, but were obliged to.