Throughout all this time, while being distrusted by the British P.O.W.s, he was reporting to MI6 by coded letters, giving guidance on targets for bomber attacks. More particularly he was engaged in subverting the German proposal to form a British Free Corps to fight for Germany. His cohorts included opera singer Margery Booth, a fellow British spy, who on one occasion whilst entertaining the camp inmates sang before Hitler just after Brown had hidden secret documents in her dress; Hitler subsequently sent her red roses wrapped in a Swastika flag. Brown was instrumental in identifying the British traitor John Amery, and both Brown and Booth had contact with William Joyce (Lord Haw-Haw), and were recruited by Joyce as a broadcaster on the German Concordia radio service; both later identified him post war, and were witnesses at his trial.