Motorists seen using the red diesel pump at the supermarket filling station had their tanks tested by HM Revenue and Customs (HMRC) officers, who were ensuring customers had the right to buy it.

Red diesel is sold at about 65p cheaper than regular fuel, known as white diesel, and can only be legally used in agricultural and industrial machinery.

HMRC said motorists have been known to take advantage of the supermarket's red diesel pumps in the past, though no offenders were caught on Thursday.

Customs spokesman Maddy Ratnett said: "Some of the time it is just lorry drivers who are filling up their refrigeration units, which is separate from the petrol tank, but we still have to make sure they don't fill both.

"It is a large country and taxpayers are the ones who pick up the costs of those who flout the law.

"Around £350million a year is lost as a result of illegal red diesel use."

Guilty parties caught with the fuel are administered with an on-the-spot £500 fine before being allowed to drive home or to a garage to remove the fuel.

Finding red diesel road users is only half the job for HMRC, as officers also search for organised crime gangs who strip the diesel of the red dye that identifies it and sell it on as white diesel.

Ms Ratnett added: "The practice of stripping the fuel is highly dangerous as it uses corrosive materials.

"It is often independent garages, many of the owners of which are innocent, who are sold fuel by these groups."

Deeping St Nicholas man John Nickols, who buys red diesel regularly for machines used by his plant hire business Superior Sales, had his car tested by officers after legally filling fuel cans with red diesel.

He said: "I appreciate being able to use red diesel in my business so I don't abuse it."