MI5 has increased the level of threat posed by Northern Ireland-related terrorism from moderate to substantial – the third most serious category out of five.
Home Secretary Theresa May said the move “reflects the continuing threat from dissident republican activity”.
In a statement to the House of Commons, she said: “As a result of this change, we are working closely with the police and other relevant authorities to ensure appropriate security measures are in place.”
The threat level to the UK from international terrorism remains at severe – meaning an attack is “highly likely”. This has not been changed.
Mrs May said the threat level in Northern Ireland was also unchanged, at severe.
She added: “The reality is that they command little support. They do not represent the views or wishes of the vast majority of people, both in Northern Ireland and the Republic of Ireland, who decisively expressed their desire for peace in the 1998 Belfast Agreement.”
Dissident republican groups such as the New IRA and Oglaigh na hEireann have been behind most of the deadly attacks on members of the security forces in recent years. They derive most of their funds through drug dealing, fuel laundering and cigarette smuggling.
In March, prison officer Adrian Ismay died when an undercar booby trap bomb detonated as he drove to work.
In 2011, Catholic police recruit Ronan Kerr was also killed when a device exploded under his vehicle while, several months earlier, in November 2012, prison warder David Black was gunned down as he drove along the M1 motorway.
The dissidents have recently claimed to have up to a tonne of “newly acquired” Semtex plastic explosive which was used widely by the Provisional IRA during the 1980s.
Democratic Unionist MP Jeffrey Donaldson expressed surprise at this latest security assessment and is seeking an urgent Privy Council briefing on the matter.
He said: “It is evident that dissident republicans are now active in Great Britain and are examining potential targets.
In Northern Ireland, the threat has been severe for some time but quite clearly this is a new development in terms of dissident republican activity.”