He joined the
Foreign Office in 1946 with the support of the
Labour Foreign Secretary
Ernest Bevin, who thought him an expert on oil transportation. He served as counsellor (and later minister) at the
British Embassy in Washington, at the time of the
Cuban Missile Crisis (1962) and the
assassination of U.S. President John F. Kennedy (1963). As Britain's special envoy to
Rhodesia (1972, 1976) he sought unsuccessfully to end
Rhodesia's Unilateral Declaration of Independence. He was
Permanent Under-Secretary (PUS) at the time of the
accession of the United Kingdom to the European Communities in 1973. His appointment as PUS had been regarded with scepticism by older hands in the
Whitehall establishment. In the event, he was liked and respected by colleagues, his managerial skills were valued and his advice was highly regarded by ministers. Created a
life peer in 1974, he sat as a
crossbencher. As head of the Colonial Office, Greenhill played a role in the
forced deportation of
Chagossians from the
British Indian Ocean Territory. Responding to Permanent Under-Secretary of State
Paul Gore-Booth's directive that "no indigenous population except seagulls" was to be left in the territory, Greenhill added that "[u]nfortunately along with the birds go some few Tarzans or Man Fridays whose origins are obscure, and who are hopefully being wished on to Mauritius etc. When this has been done I agree we must be very tough and a submission is being done accordingly." His later years included roles as governor of the
BBC and as a director of BAT Industries,
Hawker Siddeley Group,
Wellcome Foundation,
Clerical Medical and General Life Assurance,
S.G. Warburg and Leyland International. ==Honours and arms==