Career
The Right Honorary Educated at the Royal Naval College, Dartmouth, Duff started his career in the Royal Navy where he was a submarine commander during World World War II: he briefly commanded Otway and L23 in 1942 before commanding HMS Stubborn from December 1942 to July 1944. After the war Duff joined the Diplomatic Service in 1946 and served in several postings including British Ambassador to Nepal 1964-1965 and High Commissioner to Kenya 1972-1975. Having led the British official delegation to the Lancaster House talks, he became Deputy Governor of Southern Rhodesia (under Lord Soames as Governor) in 1979-1980, after which appointment he was sworn of the Privy Council, the first diplomat to be so honoured since Sir Alexander Cadogan in 1940.
Duff was Deputy Secretary at the Cabinet Office with responsibility for security matters in 1980-1984, and then Director General of the Security Service (MI5) from 1985 to 1988.