Dr Paul Nolan, who specialises in monitoring the peace process and social trends, told the BBC that he expected there would be a catholic majority within three years.
He insisted that didn’t mean a united Ireland would be inevitable as being Catholic wasn’t the same as supporting a united Ireland but he said it had important implications for unionism.
“The future of unionism depends entirely upon one thing – and I mean unionism with a small ‘u’ – it depends on winning the support of people who do not regard themselves to be unionists with a capital ‘U’,” he said.
“Does it mean one parliament in Dublin or two parliaments? One in Belfast and one in Dublin?
“I think the more that gets unpacked, the more opinion will move back and forward. Its not going to go just in one direction.”
The last census in 2011 put the Protestant population at 48 per cent, just 3 per cent more than Catholics at 45 per cent.
More recent figures from 2016 show that among those of working age 44 per cent are now Catholic and 40 per cent Protestant.
He dismissed opinion polls declaring support for a united Ireland, saying the polls ask the wrong question.
”If we got to the situation where people go into a polling booth and have to put the mark against a united Ireland, it’s very hard for anyone to predict it,” he said.
He pointed out that although 45 per cent identified as being from a Catholic background in the 2011 Census, only 25 per cent claimed an exclusively Irish identity.
“In other words people who do not identify with the traditional trappings of unionism; people who would give their support for a UK government framework and that’s a sizeable proportion of Catholics provided they are not alienated by any form of triumphalism or anything that seems to be a rejection of their cultural identity as nationalists.”
Sinn Féin President Mary Lou McDonald told the BBC unionists have to be at home in a new Ireland. “It has to be as much a home for Arlene Foster and her family as for mine,” she said.
This story first appeared in our sister site the i.