The diesel laundering plant in County Armagh contained 37,000 litres of illicit fuel and almost 21,000 litres of toxic waste stored in barrels and in an underground slurry pit.

Aside from an estimated £20m in lost revenue, the site posed a serious environmental risk.

Laundered fuel is red (or green) diesel, which has been filtered through chemicals or acids to remove the government marker. The chemicals and acids remain in the fuel and damage fuel pumps in diesel cars.

HMRC assistant director, Criminal Investigation, John Whiting said: “This is fuel fraud on an industrial scale. The sheer size of this illegal operation is staggering and far exceeds anything we have ever come across before.

“This activity would have generated massive revenue loss as well as tonnes of toxic waste – it’s economic and environmental impact on Northern Ireland would have been considerable.”

The plant, in agricultural buildings near Crossmaglen has been dismantled and a man has been arrested in connection with the find.

Alison Brown

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