Brian Arthur Field (15 December 1934 – 27 April 1979) was an English solicitor's clerk who was one of the masterminds of the 1963 Great Train Robbery. He was the crucial link between the key informant known only as "Ulsterman" (who came up with the idea of robbing the money-laden night mail train and also provided the details of the schedule and contents of the trains) with the actual gang capable of planning and carrying out such a complex and large scale robbery. He was found guilty of Conspiracy to rob, but his conviction was later overturned on appeal. Field only served time in prison for Perverting the course of justice, in relation to arranging the purchase of Leatherslade Farm, near Oakley, Buckinghamshire, which was used as the gang's hideout.