Supermarkets in the south-eastern UK presented a fresh target for motorist anger today, as reports circulated that the grocery chains had been selling contaminated fuel.

A large number of irate drivers have contacted media and consumer-affairs organisations over the past 24 hours, complaining that their cars did not run properly after refuelling at certain forecourts.

When taken for repairs, the affected vehicles were typically found to have defective "lambda sensors," used in modern car engines to regulate the richness of the fuel-air mixture. The sensor measures the amount of oxygen present in the car's exhaust gas, allowing the engine electronics to feed in the correct amount of fuel.

Such exhaust-oxygen sensors normally fail after 30,000 to 50,000 miles. This will cause the engine to use too much fuel and emit more pollution. It will often run rough at idle, and respond sluggishly or misfire when accelerating.

Automotive parts suppliers seeing unprecedented demand for replacement oxygen sensors in the South East, giving rise to suspicion that duff fuel may be involved. Some reports have hinted at ethanol contamination, but the AA said that tests have shown this is not the case. Other fuel contaminants can degrade lambda sensors, for example antifreezes or silicones.

Trading standards officers are now investing the matter. It's to be hoped they can wrap the case swiftly, lest disgruntled drivers mount a letter-bombing campaign or worse, a Downing Street e-petition. ®

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