Investigations into theft from oil pipelines in the south of England have led to the discovery of two suspected diesel laundering plants, capable of evading an estimated £12m in duty.
The plants, in Essex and Merseyside, have been dismantled by HM Revenue and Customs (HMRC).
The discovery of the plants, capable of producing 20 million litres of illicit fuel a year, is connected to activity by Kent Police investigating the theft of fuel from commercial pipelines in the UK.
HMRC, accompanied by officers from Merseyside Police, searched commercial premises in the Bootle area where they discovered a laundering plant in an industrial unit.
In coordinated activity, HMRC and officers from Kent Police searched a number of commercial premises in the Upminster and West Thurrock areas of Essex and uncovered a second fuel laundering facility.
Pat Curtis, national oils co-ordinator, HMRC, said: "Every illegal diesel laundering operation typically generates tonnes of toxic waste and robs UK taxpayers by evading fuel duty. Investigations into the seizures are continuing."
During the operation officers seized more than 100,000 litres of fuel, two fuel tankers, a 40ft curtain-sided lorry and three lorry tractor units.