 Born in Shere, Surrey, UK, Mortimer is the son of Charles Mortimer Senior, a former motorcycle road racer and proprietor of the Charles Mortimer Race School based at Brands Hatch race circuit, Kent.The school was originally named in 1963 as the Beart-Mortimer racing school, with engine tuner Francis Beart being a partner to Mortimer Senior which ended in 1965 due to Beart's other business involvements.From 1966 the venues included Cadwell Park, Silverstone and Mallory Park.