Afzal Khan, 37, smashed the previous record of £331,000, paid 18 months ago for M1, to purchase the historic F1 number plate from Essex County Council.
The Bradford entrepreneur, who owns a specialist car design company, plans to display the number plate on his £317,000 Mercedes SLR McLaren supercar.
Its first owner was the Essex county surveyor, Percy John Sheldon, who attached it to his 15hp, four-seater Panhard Levassor.
After a period in private hands it was given back to the county council in 1955 and subsequently used on a variety of civic limousines including a Darracq Torpedo, a Humber, a Daimler and a Jaguar.
The authority will use its windfall to fund an advanced driver training programme to improve the skills of hundreds of young motorists in Essex.