The two Real IRA factions in Dublin and Derry are believed to possess the greatest capability to launch an attack on Britain, the Irish Post reports.

Despite this the British Intelligence agency MI5 advised the British Government to downgrade the threat level from Northern Ireland-related terrorism from substantial to moderate last October.

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A statement from the Home Secretary Theresa May said that a "terrorist attack is possible, but not likely" to be carried out in England, Scotland or Wales by Irish Republican Army dissidents.

Commenting on the growth of the Real IRA, a senior source told the Post that many factions of the dissident group are using the organization as a front for criminality.

“There are little units here and there, but they are small in number  and it would appear they have failed  to import any sizeable munitions  from anywhere,” a senior security source told The Irish Post.

“Through decommissioning it has been established that 90 per cent of weapons and bomb making materials were handed over, that’s about as  good as you are going to get because  there are people who have been killed that previously stashed weapons.

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“The whole structure of the old  Provisional IRA is gone, the Chief  of Staff — that went with giving up the arms, and the whole general  grouping there. It’s well established  there is no Real IRA army council.

“It’s largely fundraising gangsters in Dublin and they call themselves dissident. It’s smuggling,  diesel laundering and laundering  the money they achieve in this. They’ve gone away from major robberies. You don’t hear of Dublin gangsters being stopped when they come out of Belfast, the factions are  answerable to no one really, they are  quite splintery in structure and  localised.”

Members of the Real IRA at a ceremony in Londonderry.Niall Carson/PA