Arthur S. Martin (died 1 February 1996) was a member of the British intelligence community and a primary investigator in the spy scandals in the post-war era.
In 1964, Michael Straight admitted to Arthur Martin and the U.S. Federal Bureau of Investigation (FBI) that Anthony Blunt had recruited him in the mid-1930s, while both were at Cambridge University.
John Cairncross, alleged by many to be "The Fifth Man", also admitted to Martin that he was an associate of Blunt and that he had passed papers to the Soviet government.
After Blunt confessed, it was clear that his position and his social and political connections posed a serious threat to the credibility of MI5.
Later, when Hollis and his deputy, Graham Mitchell, fell under suspicion of being GRU moles, Wilson was not informed.