He was born at Dehra Dun in India, where his father, who later joined the Eton mathematics staff, was then a Forest Officer.
Marsden was educated at St Cyprian's School, Eastbourne and Eton where he won the pulling and the sculling events as well as the mile, the half-mile and the steeplechase.
He spent four years studying for a doctorate from the University of Bonn and returned with fluency in German and French as well as good Italian, Spanish and Norwegian.
He became a Lieutenant-Colonel and commanded an independent unit working with Dwight Eisenhower's staff for the D-Day landings.
[2] Two years earlier, in 1954, he and his partner Tony Fox, astonished the rowing world by beating the Russian silver medallists in the Double Sculls at Henley Royal Regatta.