Britain has signed up to an official target of nearly 6% of all fuel sold being biodiesel by 2010.
Biodiesel is a fuel made from a combination of fossil fuel-based diesel, with a 5% mix of fuel from renewable sources, such as certain crops.
But Steve Smith, managing director of Feather Diesel Services, fears that although most manufacturers approve the use of biodiesel, in the long term, it may not be good for engines.
He told a meeting of the North East and Tyne Tees arm of the Association of Car Fleet Operators: ‘Manufacturers are saying you can use biodiesels, but the manufacturers of the injection systems don’t advise it.
‘Even if the manufacturer says you can use it, if there is a problem you could end up without it being covered by the warranty.
‘You can actually manufacturer things like fuel pumps to run with alternative fuels, but currently manufacturers are not asking for that.’