The Castle Combe circuit is used for racing with Special GT's. Norman Lackford drove such a car: a Fiat 850-BDH. He did so until 1996. I can't easily find out what happened to the engine but it looks very special:
Fiat 850 BDH van Norman Lackford

Looking at engine the block it looks more like a Cosworth, but according to the this text from the Special GT site in this picture it's still a Fiat engine:

The quick Warrior-tuned Fiat gave way to a Saxon prototype in 1996 and later a Radical which Norman is still using in the series this season (August 29 1994)