Depends...in a British city? possibly....
if they thought it would help them, I am sure they wouldnt hesitate to detonate one in the US either....
The IRA is something of a problem for me. They are socialists through and through which puts me at odds with them. Their cause however, of one Ireland is something I support whole-heartedly. What I can tell you is they would NOT detonate a device in the USA. That would be smashing the very people who they get most of their support from. They would dry up over night if they did that. They may be misguided in their politics, but the underlying cause of one united Ireland is a true cause. No, they are not tactically stupid, just misinformed.