Data from here; the cross-tabulations haven’t been released yet so one can’t know who put down which national identity with which religion, but the almost total correlation between British national identity and non-Catholic religion is glaringly obvious. As is the negative correlation between either measure and Irish or Catholic identity - although the latter far outstrips the former. It proves what I would have guessed previously - that most people choosing a ‘Northern Ireland’ identity are Catholics (or brought up as such), although significantly, in areas which are predominantly Catholic, ‘Irish’ is the preferred identity.
Omitted for the sake of not overcluttering the graph is the No religion figure, which ranges from about 2% to just over 10%, and is highest in the three districts with the fewest Catholics and the most Protestants (North Down, Ards and Carrickfergus - all to the extreme east of Belfast). What is quite remarkable, though, is the uniformity of the Northern Irish figure, across diverse socio-religious areas. I’m using the Classification 2 figure, which means people could choose multiple options, whereas the Classification 1 figure is more complicated and shows the number for each combination of options - although the only significant combination was British and Northern Irish, at 6% overall.