The system that allowed spy agency GCHQ access to vast amounts of personal data from telecoms companies was unlawful for more than a decade, a surveillance watchdog has ruled.
The Investigatory Powers Tribunal said that successive foreign secretaries had delegated powers without oversight.
But it added there was no evidence GCHQ had misused the system.
Privacy International criticised the “cavalier manner” in which personal data was shared.
The group brought the legal challenge and solicitor Millie Graham Wood said it was “proof positive” that the system set up to protect personal data was flawed.