After the trip in Italy, Tony Vandervell approached him which saw Parnell driving Vandervell's Thinwall Special (a highly modified Formula One Ferrari 375) in numerous F1 races. He left a star-studded field standing in conditions so bad that the BRDC International Trophy final raced through hail, lightning and heavy rain. With poor visibility and the track under as much as six inches of water, the race had to be stopped after six laps due to Silverstone being flooded and too dangerous to continue. When the race was abandoned, Parnell was in the lead; no official winner was declared, so although he defeated the Alfa Romeo team, it was not until two months later in the 1951 British Grand Prix that the Alfas suffered their first real defeat. After the race Reg said, "It's a pity it was stopped as I would have liked the race to have continued. I was a minute ahead of the Italians and I am sure they would not have made this up. It was like aquaplaning in an ice-cold tub, but in the cockpit it was very hot and steamy so that at 80mph I only had a dim outline of the comers and only the outlines of spray telling me that another car was in front."