William Armstrong, Baron Armstrong of Sanderstead

William Armstrong, Baron Armstrong of Sanderstead GCB MVO PC (3 March 1915 – 12 July 1980) was a British civil servant and banker.

The son of William Armstrong and Priscilla Hopkins, he was born in Clapton in London. Armstrong was educated at Bec School in Tooting and Exeter College, Oxford. From 1938 to 1943, Armstrong worked for the Board of Education and from 1943 to 1945 he was private secretary to the Secretary of the War Cabinet Sir Edward Bridges. Between 1949 and 1953, he was principal private secretary to the three successive Chancellors of the Exchequer Sir R. Stafford Cripps, Hugh Gaitskell and then R. A. Butler.

Armstrong was Under-Secretary to the Overseas Finance Division of the Treasury from 1953 to 1957, and from 1957 to 1958 of the Home Finance Division. Between 1958 and 1962, he was Third Secretary and Treasury Officer of Accounts. In 1962, he became Permanent Secretary of the Treasury and, in 1968, Head of the Home Civil Service. Due to his influence in Edward Heath's government he was called the "Deputy Prime Minister". During its dispute with the miners over the government's imposition of a Three-Day Week, however, Armstrong suffered a nervous breakdown.