There is a brief introduction explaining the themes in the literature available to date and how this thesis aims to add to available material. In chapter one I give an account of early British research into nuclear science, including collaboration between British universities and the effect the MAUD Report had on accelerating the United States atomic programme. I introduce the main British scientists here . In chapter two I focus on diplomacy between Britain and the United States in the period up to the Quebec Agreement. The two countries had their own atomic programmes at this stage and I discuss the lead up to the amalgamation of both programmes in August 1943. Chapter three examines the British raids on German heavy water facilities and the efforts to stop Germany acquiring the means to make an atomic bomb before the Allies. Co-operation between the British and U.S teams at Los Alamos is discussed, along with the crucial role played by Britain in assisting the American scientists. The British nuclear spies are featured in chapter four, focusing on Alan Nunn May and Klaus Fuchs. Their actions are discussed along with their arrests and trials. Effects of their cases on British atomic diplomacy with the Americans are highlighted. The final section sums up the legacies of Britain¿s nuclear programme and its effect on British Cold War politics with America and the U.S.S.R. The fusion, or hydrogen, bomb is mentioned briefly and an overall assessment of the achievements of the British scientists is included.