The 15th BRDC International Trophy was a motor race, run to Formula One rules, held on 11 May 1963 at the Silverstone Circuit, England. The race was run over 52 laps of the Silverstone Grand Prix circuit, and was won by British driver Jim Clark in a Lotus 25.
The 16th BRDC International Trophy was held on 11 May 1964 at the Silverstone Circuit, England
Gets the dates wrong, but this is because I switched it to the 16th iteration of this race and it doesn't explicitly state that this race continued in the later years