In 2001 , after the September 11 attacks in the U.S. , MI5 started collecting bulk telephone communications data under a little understood general power of the Telecommunications Act 1984 ( instead of the Regulation of Investigatory Powers Act 2000 which would have brought independent oversight and regulation ) . This was kept secret until announced by the Home Secretary in 2015
September 11 attacks
September 11 attacks
MI5