Between 1955 and 1956 he was employed as works manager with oil engine manufacturers Petters[2] before returning to Standard, where he achieved a series of promotions, initially within Standard, where he became General Manager from 1959 to 1962. and subsequently working for successor companies (much of the Midlands-based UK motor industry consolidated itself into what became the British Leyland Motor Corporation, late in 1968).
He resigned five months after his competitor (John Barber) to replace Donald Stokes as head of BL was appointed deputy chairman.
[8] It was announced in September 1977 that Turnbull would be joining Iran National, then assembling passenger cars based on the British Hillman Hunter.
Turnbull's mandate was to increase domestic sourcing of components and in the longer term to foster the development of a home-based auto-industry in Iran.
Remaining with Peugeot until 1984, he served as president of the Society of Motor Manufacturers and Traders from 1982 to 1984, when he joined the Inchcape investment company becoming chairman and chief executive in 1986 and retiring in 1991.