How did I miss that one!
I was at Hatfield Tech (and de Havillands) at the time, too!
The aeroplane was Druine Turbi G-AOTK, built by a group of de Havilland students, the TK Flying Group, as a successor to the series of "TK" aeroplanes designed and built at the de Havilland Technical School. If I remember correctly there was another home-made car in Paris, so they competed in a home made aeroplane and two home made cars.
Brian Hart was at DH and must have had some involvement with the engine(s) of the car(s). 1959 Hart teamed up with Len Terry to drive his Terrier Mk2 in the 1172 formula championship and won the Chapman Trophy