An ardent left-winger, Jenkins was active in the Prudential Staff Association, the National Union of Bank Employees and the actors' union Equity, of which he was assistant general secretary 1957–64. He and his wife, Marie, became active in the politics of his local community in the County Borough of Croydon, Surrey. Jenkins chaired his local Upper Norwood Labour Party and stood for the council, and Marie was elected to Croydon Council for Whitehorse Manor ward in 1949. He stood for Parliament without success in Enfield West in 1950 and Mitcham in 1955. Jenkins was involved in the Victory for Socialism group opposed to the 1956 Suez War and had been a supporter of CND and nuclear disarmament since its foundation in 1957. In 1958 he became a London County Councillor for Hackney North and Stoke Newington, serving until 1965, and he served on the London Labour Party executive in 1962. He was also involved with the Arts Council.