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John Jeffreys may refer to:John R. F. Jeffreys (1916–1944), British mathematician and World War II codebreaker John Gwyn Jeffreys (1809–1885), British conchologist and malacologist J. G. Jeffreys (1893–?), Australian schoolteacher who moved to England and founded Bryanston School in Dorset John Jeffreys, British member of parliament for Brecon and Breconshire John Jeffreys, British member of parliament for Breconshire, Marlborough and Radnorshire John Jeffreys (1706–1766), British member of parliament for Breconshire and Dartmouth