Went on to work for Coventry-Climax and was with the company when he died, aged 58. Tresilian studied at Wellington College and then Cambridge University, where he achieved an engineering degree. He then raced himself, competing in hillclimbs and cycle-cars, the former of which he first met Raymond Mays; the two would work together later at BRM. After spells working at the Prestwich motorcycle engine firm and then Rolls Royce, where he worked on car and engine design. Stewart continued racing at this time, at Donington, racing alongside the likes of Dick Seaman. He then joined Lagonda, after a spell with ERA, before becoming the head of Templewood Engineering and then Armstrong Siddeley before serving the war effort as an engine co-ordinator for the United States Air Force and the RAF. Because of his work with the former, Tresilian was due to move to the US, but instead returned to Rolls Royce after the War, before becoming an independent consultant, which included his work with BRM. As well as his Coventry-Climax work, he was also involved as an engineer with Bristol Engines at the time of his death.

Biography last updated 29 Sep 2019