Johnson raced an ERA E-Type in the immediate post-war years, taking part in the 1950 British Grand Prix in 'Taso' Mathieson's ERA E-type. He later became the chairman of this once illustrious marque. His major driving successes, however, were often achieved at the wheel of rival cars. In 1948 he won the Spa 24 Hours sports car race in an Aston Martin shared with St John Horsfall and he was second at Spa again the following year, also in an Aston, this time with Brackenbury. In 1950, now driving a Jaguar XK120, Johnson was third in the Tourist Trophy and fifth in the Mille Miglia, and a year later he came fourth in the Jaguar with Tony Rolt. Driving a Nash-Healey, Leslie finished third at Le Mans with Tommy Wisdom in 1952, and was also fourth in class (despite shock absorber problems) in that year's Mille Miglia in the same machine. Johnson collapsed with serious heart problems during the 1954 Monte Carlo Rally and it was partly as a result of this condition that he died in 1959.