Biofuel suspected in probe into diesel breakdowns
A measure intended to make diesel cleaner is being investigated as a possible cause of car breakdowns.
Fuel suppliers have to add biofuel to road fuels under the Renewable Transport Fuels Obligation (RTFO).
Radio 4's You and Yours found that this mix is being investigated after an increase in clogged diesel filters.
The Department for Transport said Transport Minister Baroness Kramer had asked the industry to resolve the issue as quickly as possible.
Diesel cars which have been affected suffer a sudden loss of power. Mechanics report the fuel filter has been clogged by a "waxing" of the fuel, similar to the effect of olive oil clouding in a bottle.
The RAC said a small number of incidents happened last winter and the problem disappeared over summer, but in November it attended 600 incidents of blocked fuel filters.
Their data suggested the breakdowns were more prevalent in eastern parts of England and Scotland, with the greatest concentration in the North East, but other parts of the country are affected.
Oxfordshire-based Jon Harvey lost power in his Citroen C3 VTR while overtaking on a dual carriageway.
He said: "I put my foot on the accelerator and it suddenly cut out.
"The mechanic said it looks like your fuel filter has got clogged and we're going to have to replace it - it cost me £160 to fix."
Major industry bodies - the UK Petroleum Industry Association (UKPIA), the Society of Motor Manufacturers and Traders (SMMT) and the Downstream Fuel Association - have all been involved in an investigation with the British Standards Institution.
David Bizley, technical director of the RAC, said the area receiving the closest scrutiny was the biofuel content of diesel, simply because the minimum amount included in diesel had been rising, and it was the newest element in a product which had worked well for so long.
He added: "Specifications have been further tightened since the problem was first reported, but it's clear that we still don't fully understand all aspects of the underlying cause."
The UKPIA represents nine oil refining and marketing companies operating in the UK.
It said it was aware of the reported problems and that the investigation being carried out with other industry bodies was all-encompassing and would continue until the cause was determined.