The plant was laundering up to 70,000 litres of illegal fuel per week

The plant, capable of processing about 70,000 litres of diesel in a week, was uncovered at Alistragh, near Armagh city in a joint operation with police officers on Wednesday night.

They dismantled and removed the equipment used in the laundering process and also seized two vehicles and 9,000 litres of illegal fuel.

It is the latest successful operation aimed at tackling the laundering of red diesel, which is sold for agricultural use at a rebated price.

The practice of removing the red dye and selling the fuel as road diesel is costing the government millions of pounds in lost revenue.

A customs spokesman said the latest purge was the fruit of agencies working together as part of the recently established Organised Crime Task Force.

"Together we have stopped a substantial amount of harmful diesel entering the fuel market and undermining honest retailers.

"As well as damaging motorists' vehicles, buying cheap diesel robs the taxpayer of money for public services," he said.