For the P25 of Formula 1, BRM chose the path of simplicity. The car complied with the new regulation which required 2.5-liter engines. The P25's 2491cc 4-cylinder engine was designed by Stuart Tresilian. The car, which debuted at Aintree in 1955, showed excellent performance, but a rather difficult behavior. In its long career, up to 1960, the P25 underwent few modifications. Meanwhile BRM had converted a P25 chassis to the rear engine, creating the basis for the P48.