Diamond became managing director of Capitol and Provincial News Theatres.
He returned to the House of Commons in a 1957 by-election for Gloucester, caused by the death of its Labour MP, Moss Turner-Samuels.
He served as Chief Secretary to the Treasury from 1964, a cabinet position from 1968, and Privy Councillor from 1965.
He represented Gloucester until his surprise defeat in 1970 by the Conservative candidate, Sally Oppenheim.
This article about a Labour Party member of Parliament representing an English constituency is a stub.