The complex relationship between religion and identity in the modern history of the British Isles is not reducible to tidy conceptual frameworks. Professor Robbins, in the most authoritative work on the subject so far, states that

The essence of the problem is that the British Isles is a religious patchwork quilt of immense complexity in which national, cultural, economic and denominational boundaries rarely achieve an exact correlation one with another. Moreover, the pattern alters over time and according to historical circumstances. Only in Ireland, it seems, is there a clear division, based on Reformation polarities, between an overwhelmingly Roman Catholic state and the rest of the British archipelago. This division, according to the Dutch geographer M. W. Heslinga, is essentially religious and represents the real frontier of the British Isles. The fact that there is a political border approximating to this division gives the argument a greater degree of plausibility. There is need for care, however, even in this apparently self-evident division. Not only is there a substantial Roman Catholic minority in Northern Ireland, but there has been a considerable Irish Catholic migration to other parts of Britain.