While Britain devotes a lot of its counter-terrorism effort to tracking and catching Islamic radicals, they still see Irish nationalists (seeking to drive the British from Northern Ireland) as the larger immediate danger. Last year there were 20 IRA (various Irish Republican Army factions) attacks planned or carried out. So far this year, there have been over 30. Worse yet, IRA factions are increasingly connecting with Islamic terror groups, and cooperating with them.
The Irish terror groups are planning violence in an effort to disrupt the peace deal that was worked out, 12 years ago, in Northern Ireland, between the Catholic and Protestant communities. British intelligence believes that about 80 Irish terrorists are planning attacks. There are far more Islamic radicals out there, but they have had much less success planning and carrying out attacks. The IRA members have more experience (over a century's worth) and can more easily blend in. The IRA have what the Islamic terrorists need, while the Moslem terrorists can provide what the IRA lacks; suicide bombers.
Although there are more potential Islamic terrorists, their planning activity has declined, largely as a result of many arrests, and failed attacks, as well as the recent al Qaeda defeat in Iraq. Islamic terrorism has also become less popular in Moslem nations over the past few years, and is less fashionable among young Moslems in Britain. The threat of Islamic terrorism is still there, but British intelligence simply believes that the Irish terrorists are trying hard to get something going again. If this merger of IRA and Islamic terrorism takes place in a big way, Britain will face a terror threat of unprecedented proportions.