A green campaigner who runs his car on vegetable oil is challenging the government over whether it should be taxed at the same rate as diesel fuel.
Mr Goodwin says the oil should be taxed at a lower rate than diesel
Kent businessman Dominic Goodwin from Maidstone runs his modified car on pure vegetable oil, on which Revenue and Customs says 47p a litre tax is due.
Mr Goodwin claims it qualifies for the 20p lower rate payable on biodiesel.
Revenue and Custom said: "Biodiesel is produced from biomass or waste cooking oil and not vegetable oil itself."
Mr Goodwin, a member of Headcorn Sustainability Group, said the cooking oil he buys from a cash and carry had been chemically tested to make sure it was suitable for his vehicle.
He said: "If the government were to encourage manufacturers to make vehicles that would run on pure vegetable oil that would be a fantastic solution to the problem of global climate change."
Green MEP for the South East, Caroline Lucas, is backing Mr Goodwin and believes the UK could be breaking EU law.
She has submitted a written parliamentary question asking the EU to clarify the status of vegetable-based bio-diesel.
"Tony Blair has repeatedly told us that tackling climate change is his biggest priority, but his government doesn't seem to be taking the same view," she said.
Revenue and Customs said its definition of biodiesel reflects the working of the Hydrocarbon Oils Duty Act 1979.
"We have concluded that vegetable oil used as a fuel substitute is not biodiesel and does not qualify for the reduced rate of duty," it said.