And that... pretty much sums it up. 1948
To add to that. AFAIK the first 'Grand Prix' was Le Mans 1906. I think this was also when the 'formula' concept was introduced, regulated engine size and minimum car weight. The first purpose built Grand Prix track was Brooklands 1907.
Set rules / formulae for the car types varied over the decades I believe.
1948 saw multiple grand prix formulae introduced, more specifically a secondary formula B, which gave rise to the labelling as A and B. Or 1 and 2 as already said.
But as too clearly said the drivers championship started in 1950 and so the first formula 1 world championship race was indeed the silverstone grand prix that year.
As also said there is some threads about this done already.
Edit - I suppose if we consider formula 1 to be the first one and only formula before a formula B was brought in, maybe 1906 was it? But not called A or 1 of course until the B came in
Edited by BullHead, 25 October 2013 - 23:53.