Brown began researching and writing Bodyguard of Lies in 1961.[3] Most of the material is based on oral testimony from Second World War intelligence personnel, as well as records from the National Archives and declassified American records (although Brown says that most of the book was written before he was able to access the latter, in 1974).[3] Brown wrote Bodyguard of Lies at a time when details of both cryptography and deception during the war were still classified. His attempts at research was resisted by the British and American governments; he was denied access to British war records and had to undertake considerable work to obtain US records via Freedom of Information requests.[1][4]