Previously secret files describe how investigators were told they faced “another 7/7″ and the loss of “British lives on British streets” if they pressed on with their inquiries and the Saudis carried out their threat to cut off intelligence.

Prince Bandar, the head of the Saudi national security council, and son of the crown prince, was alleged in court to be the man behind the threats to hold back information about suicide bombers and terrorists. He faces accusations that he himself took more than £1bn in secret payments from the arms company BAE.