It was capable of laundering over a million litres of illegal fuel per month.

Phil Rodgers Customs spokesperson

"We have found one of the biggest ever fuel laundering plants in Northern Ireland, if not the biggest.

"It was capable, we think at the moment, of laundering over a million litres of illegal fuel per month.

This is red diesel, diesel that is only supposed to be used on farms."

On Thursday, a man was arrested in connection with alleged diesel laundering in County Antrim.

An illegal fuel plant near Antrim town was closed down by the police and Customs and Excise officers on Wednesday morning.

The diesel factory was discovered following a search of a building in Islandreagh.

Officers found a 40ft trailer containing six tanks, each of which had 4,300 litres of contaminated fuel.

A jeep, a fork lift truck and a number of power tools were also recovered.

Petrol retailers from the province travelled to London recently to lobby MPs to take greater action against fuel smugglers.

The Northern Ireland Affairs Committee at Westminster is currently investigating the level of smuggling.

'Distribution network'

A recent National Audit investigation reported that six out of 10 petrol stations in Northern Ireland were selling fuel smuggled in from the Republic of Ireland.

In February, the National Audit Office revealed that petrol and diesel smuggling in the UK was costing the Treasury �830m a year in lost tax revenues.

The government spending watchdog said the problem was worst in Northern Ireland, where smuggling and legitimate cross-border shopping are costing �380m alone.

New measures will result in a tightening of control of the distribution network for rebated fuels or red diesel as it is known.

The Audit Office warned that across the UK as a whole, the main problem was the illegal use in cars of low-duty diesel intended for farm use.