[2] After the end of the Second World War in 1945, Allen left the Force as a sergeant and was chosen as an area organiser of the National Union of Distributive and Allied Workers in the year thereafter.
[2] Following its merger into the Union of Shop, Distributive and Allied Workers in 1947, he became a national officer in 1951.
[2] Allen was elected the Union's general secretary in 1962, a post he held for seventeen years until 1979.
[3] In the 1967 Birthday Honours, he was appointed a Commander of the Order of the British Empire (CBE).
[4] Allen was a member of the general council of the Trades Union Congress and in 1974 was nominated its president.