In 1974, Postlethwaite designed an all-new car for the team, the Hesketh 308, which was ready for the Silverstone International Trophy, which Hunt won, making its championship debut at the South African Grand Prix.
En 1974 Postlethwaite deseñou un coche completamente novo para o equipo, o Hesketh 308, que estaba listo para o Silverstone International Trophy, que gañou Hunt, facendo a súa debut no Campionato no Gran Premio de España.