Despite Alta's diminutive size, and their status as a primarily road car manufacturer, Alta was in fact the first British constructor to produce a new Grand Prix car following the end of World War II. Austerity limitations of raw materials did not stop Taylor beginning production of designs he had been developing throughout the war years, and the Alta GP car appeared in 1948. He also restarted production of the road-going sports cars, although without further development funding the popularity of these models rapidly dwindled. Prior to 1948, the last pre-war Alta was campaigned with varying degrees of success.

The Alta GP car was a development of the pre-war design, but was powered by a supercharged 1.5L engine, developing approximately 230bhp, and retained the 4-speed pre-selector gearbox of the prewar cars. Taylor developed the independent suspension design further, introducing wishbones and rubber linkage bushings. The first car was supplied to privateer driver George Abecassis, who campaigned it throughout 1948 and into 1949, but only finished once. Abecassis would go on to use Alta engines to power his HWM team from 1951 to 1955.

Modifications were made to the bodywork and gearchange for the subsequent 1949 and 1950 GP2 and GP3 vehicles, GP3 also gaining a two-stage supercharger. Once again they were built to order, and supplied to Geoffrey Crossley and Joe Kelly respectively. Crossley took GP2 to the 1949 Belgian Grand Prix, but could only manage seventh place. In 1950 he set a number of speed records over 50 miles, 50 km and 100 km at the Montlhéry circuit. Kelly concentrated mostly on Irish races, and his best finish was third in the 1952 Ulster Trophy. Both drivers took their respective chassis to the 1950 British Grand Prix, the first ever Formula One World Championship race. However, while Kelly finished, he was unclassified; Crossley retired with a transmission fault.

Kelly later carried out extensive modification and rebuilding work on GP3, running it as the Irish Racing Automobiles (IRA) car during 1952 and 1953. His most significant change was to replace the Alta engine with a Bristol unit.