A former computer programmer is spending his days trawling around fish and chip shops collecting used cooking oil in a bid to help save the planet.

The Scotsman reports that Alexander MacDonald converts old cooking oil into biodiesel and his business has become so popular that during the recent Grangemouth oil refinery strike he sold out in 30 minutes. Using a simple process, he converts the oil into a fuel that can go directly into the fuel tank of any diesel-powered car. It has far lower levels of harmful emissions than traditional fuel, and at 96p a litre, is also cheaper.

Mr MacDonald visits about 100 restaurants in Glasgow collecting used cooking oil that would otherwise be thrown away. He uses it to make about 4,000 litres of biodiesel a week, and has built up a dedicated band of about 200 customers, including taxi drivers, HGV drivers and regular motorists. "You get two types of customer," he said, "people who are concerned about their carbon footprint and people concerned about their pocket." He said it was impossible to tell the difference between biodiesel and ordinary fuel once it was in a car, apart from one giveaway - the lingering smell of chips when a vehicle pulls away. "It doesn‘‘t matter if it‘‘s from an Indian, Chinese or fish and chip shop, it all smells of chips," he said.

Mr MacDonald learned to convert cooking fat into biofuel in his kitchen while he was working as a computer programmer. "My kitchen was my laboratory but my partner wasn‘‘t too happy about the smell, so I got kicked out to an industrial unit," he said. "It was fun. It was like being back at high school and doing experiments." He saw the business potential, and since being made redundant 18 months ago he has never looked back. "I turned 40 and as an analyst programmer you think, ‘‘where does it all go from here?‘‘ I was interested in trying something I could be proud of environmentally and as a career. "I‘‘m not of the open-toe sandal brigade but I am concerned about what we are going to leave behind for future generations."

The first time he put the biodiesel in his van he was terrified about what would happen. "My heart was in my mouth. I was expecting it to explode or to just stop, but it just went on and on and on." He has now driven 30,000 miles in the van, all powered by biodiesel. Despite the popularity of his business, called Apple Fuels, he struggles to make a profit, and blames the level of government taxation. He has to pay 17.5 per cent of his profits in VAT, and 33.35p a litre in fuel duty. "It‘‘s galling," he said, "especially when you hear about MPs wanting to be greener."