The national furore over contaminated fuel last month could become the worst debacle over fuel quality since Formula Shell was removed from sale in the ’80s, according to the PRA’s technical consultant, Peter Barlow.

"It could turn out to be the biggest in the sense that Formula Shell was a more long-term problem, whereas this occurred instantaneously," he said.

The problems came to light when thousands of motorists complained to motoring and consumer organisations about problems with their vehicles after they had filled up at service stations in the south east - predominantly at Tesco and Morrison supermarket sites. The cause focused on unleaded fuel supplied by Greenergy and Harvest Fuels via their supplier Vopak, based in West Thurrock, on February 14. Consumer Direct received 1,000 calls within two hours of opening on the morning of Thursday March 1, from motorists reporting everything from slight juddering to cars blowing up.

While extensive coverage on TV, radio stations and national newspapers speculated over the cause - including the presence of bioethanol in the fuel - trading standards officials launched an investigation. All the companies concerned rushed out statements saying their own extensive tests had been unable to identify any problems with the fuel, and that it conformed to UK fuel standards.

Barlow, however, doesn’t believe it is anything to do with the fact the fuel is a bioethanol blend: "It’s not the fact there is bioethanol in there that would cause the problem," he stressed, "but the fact something may have contaminated the bioethanol used in the fuel.

"The fuel problems sound more consistent with there being a distribution related contamination. Something out of the ordinary must have got in there. A contaminant in the fuel would affect the oxygen sensors in an engine, which are made of very sensitive material, so it wouldn’t take much to damage them. The tests to discover what it is are very involved and will take longer than the initial tests to check that the fuel conforms to UK standards. Bioethanol has been tested sufficiently to not give anyone a short-term problem like this."