A makeshift fuel laundering plant concealed in the back of a 40ft lorry had the potential to generate millions of pounds for criminal gangs, Customs officers have said.
The lorry, seized by Customs and police in Co Antrim, is the first mobile laundering factory to be detected in Northern Ireland in several years.
Customs said the estimated annual cost to the public purse in terms of tax was over £2.5m, with the gang responsible set to make profits in excess of £2m in a 12-month period.
It contained two huge tanks capable of holding around 12,000 litres of fuel each, giving those behind the plant the capacity to produce more than 4.3m litres of illegal fuel in a year.
The fuel was destined for sale to members of the public, either straight from the lorry or through pumps at filling stations.
John Whiting, assistant director criminal investigation, HMRC, said by buying such fuel, members of the public were lining the pockets of criminal gangs, many of which police believe to be directly involved in dissident republican activity.
"Buying illicit fuel not only funds crime but also supports and encourages these dangerous activities within our communities," he said.
The mobile plant was detected after Customs officers and police carried out searches of a commercial yard in the Portglenone area on Wednesday afternoon.
Three men, from Counties Londonderry and Antrim, were arrested following the discovery.
Officers removed two large tanks chained to the inside of the trailer along with pumps and equipment used in the laundering process.
Almost two-and-a-half tonnes of toxic waste and 4,000 litres of red diesel were also recovered after searches of sheds in the area.
The massive tanks were simply strapped to the inside of the lorry, making them unstable for carriage.
It is understood measures put in place by regular fuel transporters to prevent fuel from moving around during transit were not in place.
"These tanks carrying diesel were simply chained to the trailer, showing a total disregard for other road users and posing an enormous public safety risk," said Mr Whiting.
The three men were questioned by HMRC and released on bail pending further investigations, it was confirmed.