There's always been anti-Irish sentiment in Britain. It's worth noting that for many centuries, the Irish have been the subject of British prejudices, but there was some deviation towards more virulent prejudicing when the IRA was active.

The IRA were active in the North for the best part of 40 years. Throughout the period, you'd get loyalist groups like the Red Hand Commando threatening to bomb clubs which played Irish folk music. Tensions, however, really sharpened when the IRA bombed the cities of Manchester and Birmingham. Outside of the West of Scotland where religious sectarianism was rife, this was the first instance of focused anti-Irish/anti-Catholic sentiment spilling over to a high degree in mainland Britain. The former resulted in no casualties and 212 injuries, the latter resulted in 21 deaths and up to 182 injuries.

There's a particularly good account given by a member of staff, Brian Kennedy, from the Manchester Irish Heritage Centre. He has told of how people would call the centre in the aftermath of the 1996 bombing and proclaim how they were ''dirty Irish bastards". He also recalled how the Sun newspaper were advocating boycotts of Irish products. By far the most serious manifestation of anti-Irish sentiment in the wake of the Manchester bombing was set at an Irish bar in Middleton, on the outskirts of Manchester. On the evening of the bombing, a gang of ten Loyalist men ransacked the pub, smashing up furniture and shouting the slogan, ''No Surrender''.

The Birmingham bombing was the most severe post-war bombing in Britain, and would continue to be until the 7/7 bombings in 2005. As a result, there was an upsurge in discrimination and attacks on the Irish community in the city. In a very powerful article with the Irish Times, Pat Browne - a priest in the city who was visiting relatives at the time of the bombings - had recounted how he was left stranded in Dublin after flights to Birmingham were cancelled, as staff in Birmingham simply would not handle Irish flights. People, months after the attacks took place, would still be calling local media outlets to launch a tirade against the Irish. There are plenty more touching anecdotal testaments in the Irish Times article, which I have linked. The Birmingham St. Patrick's Day parade, one of the largest in the world, was cancelled.

Source

King, Ray (2006), Detonation: Rebirth of a City