After the end of the Second World War motor racing slowly returned, based on whatever machinery could be found, largely consisting of the pre-war Voiturette cars conforming to a formula of supercharged 1.5-litre engines.

Another significant departure from previous designs was the use of twin centrifugal rather than Roots-type superchargers, developed by Rolls-Royce based on the units used on later versions of the Merlin aero engine.

Much attention was paid to keeping the centre of gravity low, and the Type 15 has a significantly lower profile compared with other Formula One cars of the time.

With the country still awash with post-war patriotism more than three hundred companies including Lucas, Girling, Rolls-Royce, Vandervell, Rubery Owen, David Brown and Standard Motors enthusiastically backed the project either with cash or help in kind in the form of parts, staff secondments, access to testing equipment and technical information.

Mays wanted to keep the car under wraps while development continued but was overruled, and after the Type 15 was revealed for the first time a major public relations operation was mounted, with articles in the press (including a very supportive leading article in The Times), features in boys' magazines, pamphlets and even a book titled "BRM Ambassador for Britain: The Story of Britain's Greatest Racing Car".

[6] A Pathé newsreel of the car's unveiling confidently declared: With all the delays the team found themselves well behind as the new World Championship began at the British Grand Prix in May.

Not being in a position to enter the race itself, Mays gave the car a demonstration run in front of the very large Silverstone crowd and donations from the public flooded in.

"All we need now is a little longer time to develop it and then we hope to show the continent what we really can do"[10] said Parnell after the race, but in truth the cold conditions had masked overheating problems that would later come back to haunt the team.

The final outing for 1950 came with a two car entry at the Penya Rhin Grand Prix, but after qualifying fourth and fifth Parnell was out early when his supercharger's drive shaft snapped before Peter Walker retired at two-thirds distance because of an oil leak in his gearbox.

For 1951 two new cars were built with improvements to the brakes, steering and fuel tanks, and were entered into the team's first full Championship Grand Prix at Silverstone.

With the thought of all the effort that had gone into the project Parnell and Walker steeled themselves to struggle on to the finish and came home in fifth and seventh, albeit several laps down on the winning Ferrari of José Froilán González.

In practice the pair were unable to run their cars to the full but set the eighth and tenth fastest times, but then Richardson's entry was cancelled on the grounds that he had insufficient racing experience.

Parnell still managed to finish second in a Ferrari entered by Tony Vandervell, who by now had grown tired of the BRM project and left to conquer Formula One in his own way, becoming a bitter rival to the BRMs.

[11] At the start of 1952 Alfa Romeo announced the withdrawal of their Alfettas from the World Championship, and with 1951 Champion Juan Manuel Fangio now a free agent Mays saw an opportunity to sign him up for BRM.

Mays invited Fangio to test the car at Folkingham, and in an all-out effort to curry favour with the busy driver he decided that having a working car on hand for testing at a time convenient for Fangio was more important than entering April's Gran Premio del Valentino in Turin, and with financial problems also weighing on Mays' mind BRM withdrew their three entries from the race.

Fangio and fellow Argentine González both started on the front row in the BRMs at the Albi GP but after running one and two both suffered overheating problems that put them out.