During the early part of the Second World War , the UK had a nuclear weapons project , codenamed Tube Alloys . At the Quebec Conference in August 1943 , the prime minister , Winston Churchill , and the president of the United States , Franklin Roosevelt , signed the Quebec Agreement , which merged Tube Alloys with the American Manhattan Project to create a combined British , American and Canadian project . The British government trusted 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 cooperation
Quebec Conference
First Quebec Conference
Polaris (UK nuclear programme)