ensor was the son of charles william ensor, a surgeon, and his wife helen margaret creighton ensor. following education at westminster school, ensor was admitted as a solicitor in 1928, finding employment with newcastle upon tyne city council in 1932. his talents as a prosecutor led to his becoming prosecuting solicitor for the metropolitan police in 1935 as well as a lecturer at hendon police college. in 1938 he was appointed clerk of the peace for the county of london.