John Duff started racing in 1920. He raced Bentleys at Brooklands and Le Mans, winning the 24 hour classic in 1924. In 1926 he raced in the USA finishing 9th at Indy in a Miller 91 and 3rd at Altoona in a 250 mile race. He retired later that year after crashing at Rockingham.
John Duff was the London agent for Bentley in the 1920s and started racing career in August 1920 at Brooklands with a 1910 Fiat S61 Grand Prix car.
In 1922 Duff was racing Mephistopheles at Brooklands. Mephistopheles began life as a 1908 chain-driven Grand Prix car, using an engine of no less than 18 litres, with two individual but linked-together cylinder blocks. Duff became the innocent party in one of the biggest blow-ups ever recorded in the entire history of motorsport. One of the cylinder blocks exploded, separated itself from the rest of the engine, and departed skywards, taking the bonnet and several other supplementary components with it. Duff rather lost interest in the car after that, and went off instead to help start Bentley's winning run at Le Mans The first of the "Bentley Boys".
Duff was atypical in that he was not particularly wealthy, and he raced Bentleys at Brooklands and Le Mans with an eye to building up his car dealership. What was characteristic about Duff was his courage and endurance. He drove a 3 Litre single-handedly for two consecutive days at Brooklands in 1922, averaging just under 90 mph. He and Clement, then head of Bentley's experimental and racing shops and a talented development and racing driver, finished fourth in the same car at Le Mans in 1923. In 1924, Duff and Clement won the race, again in a 3 Litre. Duff went on to set the World's 24 hour record at 95.03 mph with Barnato as his co-driver at Montlhery.
In 1925 he was not so lucky at Le Mans and retired with a carburettor fire after 64 laps.
When Herb Jones was killed qualifying for the 1926 Indianapolis 500, car owner Al Cotey persuaded John Duff to take on the hastily rebuilt Indy Miller. Duff started last of 28, and eventually climbed to 9th place overall at the end of the race.
Two weeks later, he took the Miller 91 to an impressive 3rd place on the fast and treacherous board track at Altoona in the AAA championship 250-mile race.
On July 5 1926, he was competing on the boards at Rockingham, when the Miller pitched him into the retaining rail. Barely escaping with his life, Captain Duff never raced again.