Acland was Principal Private Secretary to the Foreign Secretary (Sir Alec Douglas-Home, then James Callaghan) 1972–75. He was Ambassador to Luxembourg 1975–77 and to Spain 1977–79. He was Deputy Under-Secretary at the FCO 1979–82, a post which then entailed chairing the Joint Intelligence Committee. In 1982 he was promoted to Permanent Under-Secretary and head of the Diplomatic Service. Argentina invaded the Falkland Islands in April 1982 and Acland came into collision with the Prime Minister, Margaret Thatcher, over the diplomatic response. At one point during a heated discussion he threatened to resign, whereupon Thatcher backed down and said 'All right, no more Foreign Office bashing.'