An attack on Great Britain by Irish-related terrorists is a "strong possibility", Home Secretary Theresa May said today as the country's threat level was raised to substantial.
The threat assessment was increased after the head of the MI5 warned that dissident Irish republicans could attempt to mount a new wave of terrorist attacks on the British mainland.
But it was still lower than the overall threat to the UK from international terrorism, published by the Joint Terrorism Analysis Centre (Jtac), which remains at severe, meaning an attack is highly likely.
Mrs May said: "The director-general of the Security Service has informed me that he has raised the threat to Great Britain from Irish-related terrorism from moderate to substantial, meaning that an attack is a strong possibility.
"Judgments are based on a broad range of factors, including the intent and capabilities of terrorist groups."
The assessment of the risk posed by Irish-related terrorism was published for the first time "to encourage people to remain vigilant", she said.
Mrs May added: "We have been consistent in stating that the threat to the UK from terrorism is real and serious.
"The balance we aim to strike is keeping people alert but not alarmed.
"I would urge the public to report any suspicious activity to the police and security services in their continuing efforts to discover, track and disrupt terrorist activity."
The public should not expect any visible change in security measures as steps taken to deal with the international threat will also counter the threat from Irish dissident republican terrorism, the Home Office said.
Jonathan Evans, the director-general of the Security Service, said last week there had been a "persistent rise" in "activity and ambition" by dissident groups in Northern Ireland over the past three years.
While they did not have the capacity to return to the levels of violence caused by the Provisional IRA at the height of the Troubles, he said they still represented "a real and rising security challenge".
His warning came after one group, the Real IRA, publicly threatened to target banks and other financial institutions in the City of London, accusing them of "financing Britain's colonial and capitalist system".
In a speech to the Worshipful Company of Security Professionals in the City, Mr Evans said while MI5's "main effort" remained focused on international terrorism, it had been necessary to reinforce its presence in Northern Ireland to deal with the heightened threat.
He acknowledged that the recent rise in activity by dissident republicans had not been foreseen, having been assumed just three years ago to be "low and likely to decline further".
"Perhaps we were giving insufficient weight to the pattern of history over the last hundred years, which shows that, whenever the main body of Irish republicanism has reached a political accommodation and rejoined constitutional politics, a hard-liner rejectionist group would fragment off and continue with the so-called armed struggle," he said.
Since the start of the year there have been more than 30 attacks or attempted attacks on national security targets by dissident republicans, compared with just over 20 for the whole of last year, he said.
At the same time, there were increasing signs of co-operation and co-ordination between the various groups, deploying a greater variety of attack techniques with improved weapons capability - including Semtex explosives, associated in the past with the Provisional IRA which is now on ceasefire.
"While at present the dissidents' campaign is focused on Northern Ireland, we cannot exclude the possibility that they might seek to extend their attacks to Great Britain as violent republican groups have traditionally done," he said.
But he said that, ultimately, the dissidents had done little to develop a "credible political strategy" the way the Provisionals and Sinn Fein did, and many combined terrorism with organised crime, including trafficking drugs.
Asked about the Irish terrorist threat at New Scotland Yard yesterday, Metropolitan Police Commissioner Sir Paul Stephenson said he was concerned.
The Scotland Yard boss said: "Clearly we have got to be concerned by what Jonathan Evans said.
"We have got to be concerned by the information that Jonathan Evans gave us."
Earlier today, a Lithuanian judge postponed a hearing in the trial of a suspected IRA dissident accused of trying to purchase weapons and explosives in the Baltic country.
Michael Campbell, the brother of a senior Real IRA figure in Ireland, was arrested in January 2008 in an international sting operation when he allegedly handed cash to an undercover Lithuanian agent posing as a weapons supplier.
Campbell is the brother of Liam Campbell, who helped found the Real IRA and, according to Irish police, is the faction's overall commander today.
Campbell could face up to 20 years in prison if convicted of seeking weapons for terrorist purposes.
The hearing was postponed because Campbell's lawyer, Ingrida Botyriene, was ill.Reuse content