His study of engineering at Cambridge was interrupted by World War I when he was commissioned in the Dorset Regiment[4] and later served in the Royal Field Artillery.

[7] His entries with the K3 included the 1933 Isle of Man and 1934 Northern Ireland Tourist Trophy events,[8] and the 1934 Mille Miglia[9][10] He fitted a diesel engine from an AEC bus into a car built on a Chrysler chassis and used it to set high-speed endurance records at Brooklands, attaining 100.75 mph in 1933 and 106 mph in 1936.

[13] Between 1937 and 1939 he set three new land speed records, wresting them from Malcolm Campbell's Blue Bird, but was twice bettered by John Cobb.

The rivalry was friendly, and in later years Eyston, as competitions manager for Castrol, assisted with Cobb's ill-fated attempt on the water speed record in Crusader.

During World War II Eyston served on various bodies connected with industry and was a Regional Controller for the Ministry of Production.