by Jonathan Morris
BBC News Online South West
Dean Butler is tanking up his people carrier with vegetable oil for a trip to Heathrow.
Frying tonight: Dolly Knight and Jonathan Stromberg
Every day the Plymouth owner of VIP Airport Transfers does about 500 miles and the only smell from his exhaust is of fish and chips.
Dean is one of the growing number of Plymothians dropping into Plymouth Bio-Fuels to tank up.
They do it because it is cheap - 69.9p a litre - and it is a renewable resource, unlike ordinary fuels.
Plymouth Bio-Fuels, based in Plympton, renews its stock of vegetable oil every day from pubs, chips shops and leisure centres around the city.
It all goes into 1,000 litre plastic vats where it is filtered, settled, filtered again and has an undisclosed special ingredient added, before being put into the fuel tanks of people like Mr Butler.
He reckons that his fleet of five people carriers saves him £4,000 a year in fuel costs.
Dean Butler: Green fuel fan
He told BBC News Online: "I live down the road so it is easy to come here.
"It's cheaper and I like the fact that it's better for the environment than using non-renewable fuels."
If Mr Butler or other Plymouth Bio-Fuels customers cannot make it to the Plympton pumps, they can top up with ordinary diesel.
Former GP Dolly Knight, 57, and geology student Jonathan Stromberg, 35, launched Plymouth Bio-Fuels last year after several years selling products made from copper tubing to alternatively-minded people who want to improve the quality of their drinking water.
"A friend in Germany told me about it," said Mr Stromberg.
"We were on the environmental path, so it wasn't such a major step for us to take.
"We have a vision of running cars on renewable fuels."
The couple point out that the first diesel engines, patented by German engineer Rudolf Diesel in 1889, were powered by peanut oil.
The couple attended a seminar in Wales run by the Bio-Power Association and are now producing the fuel in Plymouth.
Bio-Fuel producers claim the product is less polluting than ordinary fuel
There are plans to increase supply from 1,000 litres to 2,000 litres a week soon, but Dr Knight said that there is enough waste oil in Plymouth to produce five times that figure.
Bio-Fuel, which is almost 100% used vegetable oil, is related to bio-diesel, which is a combination of ordinary diesel and vegetable oil.
Producers of both fuels are banned from using unused vegetable oil because there is no fuel tax on it.
But Bio-Fuel gets the same 20p a litre tax discount from the government which means that although it is more expensive to produce than ordinary fuel, its price can be kept low.
For drivers to make the switch to Bio-Fuel, the firm offers advice and equipment including uprating filters, fuel pumps and installing fuel heaters at a cost of about £200.
Bio-Fuel takes five weeks to produce
Bio-Fuel when cold is thicker than ordinary diesel and so clogging can occur if it is not heated.
But when warmed it can also pick debris from diesel tanks which can also cause problems.
The firm also warns drivers that they do not accept any responsibility for damage caused by the fuel.
However, the couple are adamant that any diesel car can run trouble-free with their advice and the right equipment, although new cars could have their warranty affected by using Bio-Fuel.
Dr Knight maintains that her own Audi TDi estate has run without any trouble on vegetable oil.
She said: "We ran the Audi for several months before deciding we could market the fuel.
"We treat every customer individually so we look at their requirements and advise them accordingly.
"We do the modifications and we give them 100% support of anything happens."
The couple are now hoping to expand and they see a future of other outlets like theirs.
Plymouth Bio-Fuels is the only outlet in Devon and there are only about 30 Bio-Fuel factories around the UK at the moment, but they are increasing in number with the support of environmental groups like Friends of the Earth.
Back at the fuel pump, Mr Butler is setting off to Heathrow, powered by the left-overs from his own local fish and chip shop.