Liberty, the civil rights group that brought the case, claimed the ruling meant that British spies had acted illegally by “accessing” data about the public. The claim was strongly denied by the Government, which said no requests to the Americans to spy on people had ever been made.

The tribunal found the regime was unlawful up to last December, when decisions were made to publish details of practices, which made them lawful.

Liberty said it would now go to the European Court of Human Rights to prove that these “limited safeguards” were not adequate.