The organisation responsible for the worst single atrocity of the Troubles had a membership of 150 hardcore, experienced terrorists and was funded by fuel and tobacco smuggling, Belfast High Court heard yesterday.
The Real IRA, the terror group behind the Omagh bomb which killed 29 people and unborn twins, also received financial and logistical support from another 250 republican sympathisers dissatisfied with the Good Friday Agreement who were willing to carry out criminal activity on terrorists' behalf.
The assessment contained in intelligence documents compiled by the British Embassy also concluded that support for the dissidents was concentrated in south Armagh, Londonderry and Belfast.
The papers, signed by David Watkins, senior director for policing and security in the Northern Ireland Office, were sent to the Department of State in the US sometime around 2000 or 2001 and stated that RIRA units were at that time still committed to continuing the republican campaign of violence and undermining Northern Ireland's fragile peace.
The reports were read to Belfast High Court during day 10 of a landmark civil suit being brought against five men believed to be behind the Omagh bomb.
Michael McKevitt, Liam Campbell, Seamus Daly, Seamus McKenna and Colm Murphy all deny any involvement in the bombing.
In court yesterday Brett Lockhart QC, a lawyer acting for the six families involved in the multi million pound case, said the British assessement was that the RIRA's reason d'etre was to "supplant the Provisional IRA as the largest republican terrorist organisation".
Funding of about £100,000 or £150,000 was donated to the RIRA by sympathetic benefactors in America, the court was told.
Mr Lockhart told the court the RIRA was believed to be responsible for bomb attacks on a number of Protestant towns including Moira, Banbridge and Lisburn throughout 1998.
The fledgling terror group were also thought to be behind mortar attacks on the MI6 headquarters, BBC television centre and Hammersmith Bridge in London as well as in Glassdrummond and Armagh city.
The court heard how links between the RIRA and other dissident republican groups were exploited sporadically through personal acquaintances rather than any formal agreements.