Mr. Macmillan speeded the tests so that Britain could make sure her weapons worked before beginning talks with Russia and America about the banning of nuclear weapons.

Even as the bomb was being exploded Mr. Macmillan was telling the Commons: "I am determined we should be and remain a nuclear Power."

Although the "trigger" date was one of Britain's most closely guarded defence secrets, it had been generally believed that it would not be until next month at the earliest: