Development of the FW03, the Williams FW04, in a single example, was designed by Ray Stokoe. Equipped with the V8 Cosworth engine, the car obtained as its best result a second place at the 1975 German GP with Jacques Laffite, who cleverly knew how to exploit the problems of the most accredited teams. The FW04 was then sold to Brian McGuire in 1976, who used it in some English national races and in 1977 renamed it McGuire BM1.