The mathematician Shaun Wylie was one of the leading members of the Bletchley Park code-breaking team of the Second World War as well as one of its last survivors.

Shaun Wylie was born in Oxford, the son of Sir Francis and Lady (Kathleen) Wylie; his father was the first Warden of the Rhodes Trust. He was educated at the Dragon School and Winchester College, from which he won a scholarship to New College, Oxford, where he studied mathematics and classics. In 1934 he went to Princeton University, studying topology — roughly, “rubber-sheet geometry”, or the study of properties invariant under continuous deformation — under the great American mathematician Solomon Lefschetz (1884-1972). He took his PhD in 1937, and became a Fellow of Trinity Hall, Cambridge, in 1938-39. Wylie was an excellent chess player, and very good at anagrams — both skills relevant to the next phase of his life.

While in Princeton, Wylie had met the British mathematician Alan Turing (1912-54). When war was declared in 1939 Turing joined the mathematical team of the Government Code and Cypher School at Bletchley Park, working on deciphering German military radio traffic. In late 1940 Turing invited Wylie to join him. In February 1941 Wylie joined Turing’s team in Hut 8, working on the Enigma machine used by the German Navy. In the words of Hugh Alexander, Turing’s successor as head of Hut 8, “except for Turing, no one made a bigger contribution to the success of Hut 8 than Wylie; he was easily the best all-rounder in the section, astonishingly quick and resourceful and contributed a great deal to theory and practice in a number of different directions”.

In autumn 1943 Wylie transferred to work on German teleprinter traffic, generated by the Lorenz machine, codenamed Tunny. The electronic machine Colossus developed to decipher Tunny was a precursor of the modern computer; Wylie’s work on Tunny continued even after VE Day on May 8, 1945.

While at Bletchley Park Wylie met and was married to Odette Murray, a Wren also working in his section.

Wylie returned to academic life after the war; he was a mathematics Fellow at Trinity Hall till 1958. While not prolific in publishing research, he was outstandingly successful as a lecturer, and as a tutor at Trinity Hall, where he was described by one of his grateful pupils as “the most human of beings”. He was also a very successful doctoral supervisor. His first student, William Tutte (1917-2002) had also worked on Tunny at Bletchley Park. Tutte went on to become a Fellow of the Royal Society. With Peter J. Hilton, Wylie published the book Homology Theory: An Introduction to Algebraic Topology in 1960. “Hilton and Wylie” has gone on to become a classic; through his book and his students, Wylie is recognised as one of the founders of the outstanding British school of algebraic topology.

In 1958 Wylie became Chief Mathematician at Government Communications Headquarters in Cheltenham, the successor to the Government Code and Cypher School of his war work. While his work there was secret, one publicly visible outcome was his involvement in the work of his GCHQ colleague James H. Ellis on public-key cryptography.

On retiring from GCHQ in 1973, Wylie ended his career as he began it — in schoolteaching. He taught mathematics and Greek at Cambridgeshire High School for Boys (later Hills Road Sixth Form College) in Cambridge till 1980. He was elected an Honorary Fellow at Trinity Hall on his retirement.

The Ultra Secret — the fact that Allied intelligence had successfully broken German military radio codes — was not only top secret during the war, but, as a result of a decision made by Churchill in his last months as Prime Minister, remained so for nearly 30 years afterwards. Everyone who had worked at Bletchley Park had signed the Official Secrets Act, which continued to bind them to secrecy. Partly as a result of the publication in 1974 of F. W. Winterbotham’s book The Ultra Secret, old Bletchley Park hands eventually began to speak out, notably Turing’s statistical assistant Jack (Professor I. J.) Good (obituary, April 16). Wylie wrote an account Breaking Tunny and the Birth of Colossus, published in 2001. He also appeared in several television programmes, where his contributions were notable not only for their technical content and historical importance, but also for his strikingly warm and engaging personality and sense of humour. Bletchley Park — Station X, in wartime terminology — is now a museum; Wylie and Odette were among those interviewed for Station X material.

Wylie had many interests outside mathematics. In addition to chess and anagrams, he was an international hockey player, representing Scotland in 1938, and a keen long-distance walker. He composed crosswords for The Listener, as Petti (a play on his name — “wyliecoat” is an old Scottish term for petticoat). He had a lifelong interest in amateur dramatics, and was president of the dramatic club at Bletchley Park. He was a founder member of the Social Democratic Party, and continued as an active supporter of the Liberal Democrats.

Wylie was a modest man, of great human warmth. When asked whether he had any regrets, he replied: “I wish I’d been a better mathematician.”

His wife Odette predeceased him, as did their eldest son. He is survived by two sons and a daughter.

Shaun Wylie, mathematician and code-breaker, was born on January 17, 1913. He died on October 2, 2009, aged 96