A "dangerous" fuel production plant capable of producing over 240,000 litres of illicit fuel a year has been raided and shut down.
If the fuel produced by the plant was sold legally it would raise £120,000 in duty a year, according to HM Revenue and Customs (HMRC).
The plant was uncovered in a raid on an industrial estate in Tilbury, Essex, by HMRC.
Those running the illegal operation attempted to clean contaminated fuel which was then sold to motorists from the back of a transit van.
The fuel is usually filtered through chemicals or acids to remove the contamination and make it appear normal.
But the chemicals and acids can remain in the fuel and damage the fuel pumps.
Clare Merrills, from HMRC, said: "HMRC takes the dangerous and illegal practice of storing and selling contaminated fuel very seriously. The chemicals and fuels stored and sold from this site were unsafe and the dangers they pose to anyone in the vicinity show a total disregard for public safety.
"There is no benefit to the general public from this activity and every motorist using illegal road fuel runs the risk of destroying their engine and having their vehicles seized. So filling up with fuel that is being sold at a cheap price could in fact cost more in the long run."
Over £200,000-worth of equipment used for cleaning the contaminated fuel, including pumps and storage tanks, was seized by HMRC.
The van used to transport the fuel, complete with a pump, a meter and 20,000 litres of contaminated petrol, kerosene and bio-fuel were also seized.