Criminal gangs, with links to Irish loyalist paramilitary groups and the Real IRA, are believed to be behind a flood of illegal fireworks into Britain and the Irish Republic.
Northern Ireland security sources say they are investigating the possibility that one or more of the area's numerous criminal gangs are involved in large-scale illicit trade in fireworks.
A separate senior source within the British fireworks industry confirmed this and said that security services and police were investigating the large-scale smuggling of fireworks into Britain by gangs linked to paramilitaries.
Security sources said they were not in a position to say with absolute certainty that a criminal gang was involved in supplying fireworks to Britain, though they added that gangs based in Northern Ireland certainly had links with crime outside the area. One Belfast source said: "We can't say definitely that people from here are involved with this on the mainland, but we wouldn't be at all surprised."
Security officials are on alert in the run-up to Hallow-e'en and Guy Fawkes Night and are already investigating the discovery in August of a 400-ton haul of illicit fireworks, the largest seizure ever made in Northern Ireland. They were stored in 12,000 boxes on 12 40ft container lorries found in a village in County Antrim.
And in July this year, a group of armed men held up police officers who were examining a van containing fireworks, counterfeit CDs and DVDs in County Louth, just south of the border. The gang took back these goods, which had been seized earlier by the authorities, and then disappeared.
A fireworks industry source said the industry was liaising with security officials to combat the illegal trade in fireworks. He said: "The security services are obviously reluctant to go public on this but they have indicated to us that loyalist paramilitaries are involved with the illegal trade in fireworks and these are being smuggled into mainland Britain to raise funds."
Last week, The Independent on Sunday reported that an estimated 2,000 tons of fireworks are being sold illegally every year.
The biggest haul ever found in Britain was uncovered earlier this month in Cardiff. South Wales police seized a 60-ton stockpile of illegal fireworks. In Merseyside in recent weeks, 27 telephone boxes and eight cars have been blown up using the gunpowder from fireworks. In Liverpool city centre, a car bomb outside a nightclub and a nail bomb thrown into a pub were both found to contain components from fireworks.
A House of Commons report earlier this year estimated that dissident Republicans and the Provisional IRA had a combined income capacity of around £10m. The Organised Crime Task Force, based in Belfast, estimates there are 76 criminal networks in Northern Ireland, some involving former or current members of paramilitary groups. Much of their income comes from smuggling goods across the border.