 He was a government whip from 1974 to 1976, and junior Northern Ireland minister from 1976 to 1979.In 1980, he was convicted of shoplifting a map valued at 60 p from a shop in Artillery Row and goods valued at £14.53 from the Army & Navy Stores in Victoria while taking anti-depressant drugs.In 1981, Dunn was among the Labour MPs who defected to the new Social Democratic Party.