During the early part of the Second World War , Britain had a nuclear weapons project , code-named Tube Alloys , which the 1943 Quebec Agreement merged with the American Manhattan Project to create a combined American , British , and Canadian project . The British government expected that the United States would continue to share nuclear technology , which it regarded as a joint discovery , but the United States Atomic Energy Act of 1946 ( McMahon Act ) ended technical co-operation . Fearing a resurgence of United States isolationism , and Britain losing its great power status , the British government resumed its own development effort . The first British atomic bomb was tested in Operation Hurricane on 3 October 1952 . The subsequent British development of the hydrogen bomb , and a fortuitous international relations climate created by the Sputnik crisis , facilitated the amendment of the McMahon Act , and the 1958 US – UK Mutual Defence Agreement ( MDA ) , which allowed Britain to acquire nuclear weapons systems from the United States , thereby restoring the nuclear Special Relationship
Operation Hurricane
Operation Hurricane
Trident (UK nuclear programme)