OWNERS of fast sports cars are not well-known for their concern for the environment.

But David Lewis is hoping to lead them to green paths with a conversion kit that allows high-performance cars to run on a mixture of propane (LPG) and diesel.

Known as "fumigation", the system has been used for more than 25 years in the US for large trucks and agricultural equipment.

Mr Lewis, who estimates he owns about 20 cars - including two race cars - previously ran an Italian car salesroom and garage, Forza Italia, in Standlake Business Park, Witney Road, but is now based in Oakley.

The motosport fan, who was formerly an international rally driver, has modified the system to work with the more sophisticated and advanced diesels found in Europe.

A switch on the dashboard allows propane to enter the engine after it has started, increasing the power and cutting fuel consumption.

His company, Advanced Fuel Technologies, is supplying an Alfa Romeo 2.4 for a Channel 5 TV car programme to race on biodiesel with propane, at the Castle Coombe race track in Wiltshire.

Mr Lewis tested a 2.4-litre vehicle and found fuel consumption over a six-month period moved from an average of 30mpg to nearly 40mpg.

He said: "I have been in motor racing and I was getting a bit embarrassed about the amount of pollution that I have been cooking up in my life.

"This completely eliminates the black smoke that comes out of a diesel exhaust, and after a few dozen miles the engine oil becomes cleaner."

He says he has so far converted about 30-40 vehicles, including a motorhome. "Everyone wants to know why it has not happened before."

A supplier to the United Nations is considering ordering the kits for Afghanistan, he said, where vehicles are struggling to run on the local diesel.

The propane would be supplied in cylinders, since LPG is not available in filling stations there. Eventually he hopes to have a string of dealers offering the kit, which sells for £495, plus VAT, and takes three hours to fit.