As it will be, I hope, for you to read.
The late 1920s saw a dramatic upsurge in popular concern about the abuse of police powers in Britain, the end result of a longer-term trend. Various aspects of policing were seen as worrying, but the most important concerned illegitimate forms of questioning. The phrase ‘the third degree’—imported from America—came to encapsulate this unease. Before the First World War, the terminology began to be used in British coverage of American crimes and their investigation, typically accompanied by disparaging commentary on American methods as well as the confident assertion of the superiority of British policing. The wartime growth in police powers and broader state regulation caused some to see an erosion in the ‘liberty of the subject’, and a series of scandals seemed to reveal serious problems with police procedure. The popularity of crime dramas featuring ‘third-degree’ interrogations also shaped public images of the police. Scandals in 1928 generated enough of an outcry to force the calling of the Royal Commission on Police Powers and Procedure (1928–29). Even though few concrete procedural changes were undertaken, it appears to have successfully calmed worries about the police, which receded and did not reach a similar level until the late 1950s.
The article: full-text; PDF.
(For those of you interested in such things: when the published, paginated version appears, the links will, I am informed, be updated.)