Although it was clear from constituency level results and polls before the referendum that Catholics were far more supportive of the EU, this is the first scientific data to put a figure on that support.
The numbers have emerged from an Ipsos-MORI poll which involved a very large sample of 4,000 – four times that used by most professional polls.
The research, which was conducted on behalf of Queen’s University, shows that 60% of Protestants who voted supported Brexit, but a large minority of 40% wanted the UK to Remain in the EU.
Among those who described themselves as unionists, 66% said that they voted to Leave, while 88% of nationalist voters said they voted to Remain. Of those who described themselves as neither unionist nor nationalist, 70% voted for Remain.
On the nationalist side, there was unanimity from the two major political parties, Sinn Fein and the SDLP, in support of the EU (although some dissident republicans and other non-violent smaller groups did not support that stance).
By contrast, the main unionist parties were split, with the DUP calling for a Leave vote while the UUP adopted a Remain position (although many UUP members spoke out in support of Brexit). The smaller TUV and Ukip also supported a Leave vote.
Almost two thirds of those who identify as ‘Northern Irish’ voted to stay in the EU.
The results also show the difficult task faced by the leadership of the DUP and UUP, with sizeable sections of each party’s support not going along with their leadership.
In the DUP – whose economy minister, Simon Hamilton, has repeatedly refused to say how he voted in the plebiscite – some 30% of the party’s supporters voted Remain. And in the UUP, there was an even starker position, with a majority of members – 54% – supporting Brexit, despite leader Mike Nesbitt’s support for Remain.
By contrast, 91% of TUV supporters voted to Leave and 95% of SDLP supporters voted to Remain.
The interviews – which were funded by the Economic and Social Research Council of the UK – were conducted both before and after the 23 June referendum, taking place between 6 May to 9 August.
Meanwhile, on Monday the Assembly will debate an SDLP proposal to endorse an Irish Government suggestion that “there should be legal recognition of the unique status of Northern Ireland and the circumstances on the island as part of the arrangements to leave the European Union”.
The SDLP motion – which will merely express the opinion of the Assembly rather than having any direct effect – states that such a status “can safeguard the interests of the people of Northern Ireland”.