Cottell's first civil engineering position was with Hampshire County Council but he also worked for public bodies in Gloucestershire, Northamptonshire and Berkshire where he designed and supervised schemes that included the Oxford Western Bypass and the M4 between Hanbrook and Tormarton.
Cottell's first civil engineering position was with Hampshire County Council and he was elected a member of the Institution of Civil Engineers (ICE) in 1958. During this time he also worked for the Gloucestershire, Northamptonshire and Berkshire County Councils and contracts he was involved with include the Oxford Western Bypass and the M4 motorway between Hanbrook and Tormarton.