Criminals involved in the illegal fuel trade could be escaping justice because they are being tipped off by rogue officials ahead of raids, it has been claimed.
Fuel smuggling is believed to have cost the UK government £70m in lost revenue during 2012.
But despite hundreds of raids over the past decade, nobody has been jailed in connection with fuel fraud here for 11 years.
Yesterday the Northern Ireland Grand Committee of MPs, sitting at Stormont, heard the scam described as "atrocious criminality".
The committee heard 50% of all fuel bought in Northern Ireland can be traced back to smugglers.
Concern was expressed by several MPs about the lack of progress in punishing the crime bosses involved in laundering.
East Antrim MP Sammy Wilson said it seemed some criminals had advance knowledge of raids.
"Although we have a record number of raids on fuel laundering plants, we still don't have arrests," he said.
"It almost seems that the smugglers are aware that these raids are going to occur and so they leave their booty behind but they themselves escape."
North Antrim MP Ian Paisley junior (right) questioned if "insiders within the services" are tipping off smugglers.
"Statistics show that 50% of all fuel bought in Northern Ireland has an illicit trace," he said.
"That is an atrocious amount of criminality in terms of local fuel smuggling."
Earlier this year it was claimed that former IRA chief of staff Thomas 'Slab' Murphy was tipped off four hours before he was to be raided in a major cross-border police swoop.
Detectives found evidence that Murphy and his associates knew about the operation and destroyed computers and documents before the raids took place in March.
Upper Bann MP David Simpson described the issue as "a running sore" in Northern Ireland.
"I understand that as of last week 47 people have been interviewed by the police but no-one has yet served any time for this crime," he said.
Minister of State Mike Penning said there had been some recent successes in closing down plants.
Illicit sales in the province currently account for an estimated 12% of sales – down from a high of 40% six years ago but still much higher than the average in Britain of 4 or 5%.