UK attack by dissident republicans 'a strong possibility'
A terror attack in Britain by dissident republicans is now a "strong possibility", according to a new security assessment.
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 and have been transforming Northern Ireland ever since.
"However it is sensible, given their stated aims, that the public in Great Britain should also remain vigilant and report any suspicious activity to the police.
"But we should not be alarmed, and this should not affect how we go about our daily lives."
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.
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, s everal months earlier, in November 2012 prison warder David Black was gunned down as he drove along the M1 motorway.
In March 2009, the Continuity IRA shot dead police officer Stephen Carroll in Co Armagh just days after the Real IRA gunned down two soldiers outside a Co Antrim military camp.
The dissidents, who derive most of their funds through criminality, such as fuel laundering and cigarette smuggling, command little community support but retain a tight grip in certain areas through fear and punishment attacks.
They are heavily infiltrated with informants and have recently been hit by a number of high profile arms finds and arrests.
However, police in Northern Ireland have cautioned that their capabilities, in isolated incidents, could be increasing as they acquire more sophisticated weaponry like mortar bombs and high calibre assault rifles.
Dissidents have also claimed to have up to a tonne of "newly acquired" Semtex - the odourless 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.
The Lagan Valley MP said: "It is evident that dissident republicans are now active in Great Britain and are examining potential targets. Obviously that's a matter of concern.
"We had no prior indication that the threat level had been increasing. 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."
Ulster Unionist MP Tom Elliott said the raised threat level reinforced the need for vigilance.
"This is not a decision the security services or Government will have taken lightly. People need to know which organisations are now posing an increasing threat to the security of the United Kingdom and what level of co-operation there is between these groups.
"Irish republican terrorists have murdered and created destruction for years. We don't want any more of these actions, it is time people were allowed to get on with their lives," said Mr Elliott.