At the end of the war in 1945, Smith returned to the UK, where he was appointed as a radio producer in the BBC features department by Laurence Gilliam. According to features producer Douglas Cleverdon, Gilliam "genially tolerated" Smith's Communist Party membership. In 1947, he was identified by MI5 as a "secret member of the CPGB" (Communist Party of Great Britain) and part of a communist cell at the BBC in 1947, and as a result his movements were followed and his telephone bugged. An MI5 officer noted that "Reggie has paraded his opinions (so) flamboyantly that his friends thought that he was consequently in danger of losing his job." Indeed, as the Cold War developed, fears of a communist in the features department led him to being transferred to the drama department in 1954. Following the Soviet invasion of Hungary, Smith resigned his Communist Party membership. Given a free hand and liberty, Smith flourished as a radio producer, in what is considered a golden period for radio. Important work from his BBC days include "The Easter Rising, 1916" (1966) about the Irish uprising, and "The Pump" (1972), a documentary about a major heart operation. He was a kind, generous and enthusiastic man, well known for finding parts in his productions for anybody who seemed to need one. Harold Pinter and Richard Burton were among those he helped in the early days of their careers. He was also well known for his passionate enthusiasm for chess, cricket and rugby, and he would sometimes disappear from a production midway through the day to attend a match.