AT THE Post Office Research Station in Dollis Hill, North London, from 1936 to 1974, Arnold Lynch specialised in the measurement of the electrical and magnetic properties of materials. Both during and after the war his work greatly assisted the drive towards miniaturisation of radio and radar sets. It was also crucial to one of the most complicated codebreaking sagas of the war — the cracking of the Fish code, an exceptionally complex teleprinter cypher used by the German High Command.

Lynch’s work on the development of an optical tape reader was essential to the construction of the Colossus machine which was used to break Fish. The Colossus has a serious claim, too, to be considered the first programmable electronic computer.

Arnold Lynch was born in Tottenham, North London, in 1914. His father was headmaster of West Green School and both parents were very active in the Labour Party. He won a scholarship to Dame Alice Owen’s School in Islington, before going up to Emmanuel College, Cambridge. Shortly after graduating he entered the Post Office by competitive examination.

In 1943 he was studying photocells. Unknown to him, his boss at Dollis Hill, Tommy Flowers, was working to develop a machine that would break Fish — manual decoding was so slow that any coherent material it yielded was already hopelessly out of date. Thanks in large part to Lynch’s work on optical tape readers, the Colossus could read punched tape at 5,000 characters per second, five times faster than previous designs.

After the war he continued to research dielectric loss. He felt it was a great professional achievement when this work led to the choice of British polyethylene in preference to American in the first transatlantic telephone cable laid in the mid-1950s.

When he retired in 1974, he returned to the lab work. At City University he developed the measurement technique now used to meter electricity flowing in the high-voltage link between the British and French national grids. He worked in the electrical engineering department of University College London, using open resonators for millimetre-wave measurements. He also worked on a new free-space method of measuring ferrites. A paper on the subject, with several co-authors, won the Maxwell Premium of the Institution of Electrical Engineers.

Lynch’s major work in retirement was at the National Physical Laboratory in Teddington, again on precise electrical measurement. He developed a non-contact method of measuring the electrical resistivity of metals, which greatly facilitates the testing of aircraft components for correct heat-treatment and is also used to identify coins in coin-operated machines.

One of his great interests was the history of technology, and he was a member of the archives committee of the Institution of Electrical Engineers for some 25 years. He took a great interest in the project, begun in 1994, to rebuild Colossus at the Bletchley Park Museum.

He married Edith Taylor in 1953. She died last year, and he is survived by a son and a daughter. Another daughter died in infancy.

Arnold Lynch, electrical engineer, was born on June 3, 1914. He died on November 13, 2004, aged 90.