[g]Das erste zu der neuen Formel-1-Weltmeisterschaft zählende Rennen wurde am 13. Mai 1950 in Silverstone (England) als Großer Preis von Großbritannien ausgetragen.[/g]
The first Formula One World Championship was won by Italian Giuseppe Farina in his Alfa Romeo in 1950, barely defeating his Argentine teammate Juan Manuel Fangio. However Fangio won the title in 1951, 1954, 1955, 1956 & 1957, his streak interrupted after an injury by two-time champion Alberto Ascari of Ferrari. Although the UK's Stirling Moss was able to compete regularly, he was never able to win the World Championship, and is now widely considered to be the greatest driver never to have won the title.[3][4] Fangio, however, is remembered for dominating Formula One's first decade and has long been considered the "grand master" of Formula One.[citation needed]
from german wikipedia
so it was in 1950 13th of may