Denied the chance to race abroad by World War II, Whitworth competed in numerous races in the United Kingdom. In 1935 and 1936 he competed in the Manx Grand Prix, but retired both times. In 1937 he competed in the Isle of Man TTfor the first time, which was thought at the time to be the toughest race in the world. In the 250 cc Lightweight TT race, he competed on a Cotton motorcycle but failed to finish. He failed to finish in 1938 as well, but in the 350 cc Junior TT he came sixth on a Velocette. In the 500 cc race at the Ulster Grand Prix he finished third, behind Jock West and Ginger Wood. In 1939 he finished fifth in the Junior TT and twelfth in the 500 cc Senior TT, in which he competed for the first time. In the first post-war TT in 1947, Whitworth finished second to his teammate, Bob Foster, in the Junior TT, the best TT result of his career. He retired from the Senior TT race. In, Whitworth took part in the newly created World Championship. At both the Dutch TT and the Belgian Grand Prix, Whitworth finished fourth in the 350 cc class resulting in sixth place in the overall championship standings. Outside of the championship, Whitworth won the 350 cc race at the French Grand Prix in Saint-Gaudens. In the season, Whitworth took eleventh and nineteenth places in the Junior and Senior TT respectively. For the Senior TT, he competed for the first time as a works rider, for Triumph.
Fatal accident
On 2 July1950, Whitworth competed in the 350 cc BelgianGrand Prix at Spa-Francorchamps. He was riding a privately entered Velocette and was in a fight for fifth place with Harold Daniell, Ted Frend and Charlie Salt. On the tenth lap, Whitworth and Salt came together, crashing heavily. Whitworth was taken to hospital where he was diagnosed with a skull fracture. The following day, Whitworth died in hospital from his injuries. In accordance with his wishes, which were to be buried close to the scene of any fatal accident he might have, he was buried in the local cemetery in Spa.
