A woman has been arrested following the discovery of fuel laundering plant in Co Armagh - capable of producing almost 3.6 million litres of illegal diesel each year.
The plant - which could have cost the Exchequer as much as £2 million a year in evaded taxes - was uncovered in Co Armagh on Wednesday.
HMRC officers and police removed some four tonnes of toxic waste - a by-product of the fuel laundering process - as well as plant machinery.
A woman arrested has since been released on police bail pending further enquiries.
Mike Parkinson of HMRC said the buying of illegal fuel "not only funds crime, it also supports and encourages these dangerous activities within our communities".
"The closure of this operation means we have stopped a large amount of illicit fuel entering the
legitimate market, preventing further revenue loss and helping law-abiding traders fight unfair competition," he said.
"These are difficult times for businesses economically and it is impossible for legitimate traders to
compete on an unfair playing field. We owe it to them to support them in any way we can."
The latest seizure comes only weeks after customs officials shut down a diesel laundering plant capable of producing over 22 million litres of illicit fuel a year
The plant was capable of producing enough fuel to evade almost £14 million a year in tax.
HM Revenue and Customs and PSNI officers made the discovery as they raided an isolated farm building in the Jonesborough area of south Armagh in May.
During the operation officers removed over 26 tonnes of toxic waste – the by-product of the laundering process – and 700 litres of illicit fuel, as well as vehicles, pumps and equipment.
More than 100 fuel-laundering plants have been raided in Northern Ireland in the last three years.
But the authorities have faced criticism over the fact that no-one has been jailed for the crimes.
Last December Justice Minister David Ford introduced legislation that may increase the likelihood of custodial sentences in the future.
The law change handed the Director of Public Prosecutions in Northern Ireland the power to appeal over sentences for excise evasion through fuel and tobacco smuggling on the grounds of undue leniency.