A faith is something you die for, a doctrine is something you kill for. There is all the difference in the world.

Both his grandfathers John Benn (who founded a publishing company) and Daniel Holmes were also Liberal MPs (respectively for Tower Hamlets Devonport and Glasgow Govan). " Since leaving Parliament Benn has become involved in the grass-roots politics of demonstrations and meetings and has been the President of the Stop the War Coalition for the last decade. In the period when the Labour Party was in Opposition for a year he was the Chairman of the Labour Party.

In the Labour Government of 1974–1979 he returned to the Cabinet initially as Secretary of State for Industry before being made Secretary of State for Energy retaining his post when James Callaghan replaced Wilson as Prime Minister. He has been a vegetarian since the 1970s.