Up to four referendums would have to be held to unite Ireland, according to an academic studying how polls on Irish unity would be best carried out.

The study is being led by the constitution unit at University College London (UCL), with help from University College Dublin, Trinity College Dublin and Queen's University Belfast.

Dr Alan Renwick, leading the project, suggested that a referendum would have to be held in both parts of Ireland before and after a deal was brokered.

"The Good Friday agreement explicitly mentioned one referendum, which is the referendum in the North," he explained.

"It seems to imply that that takes place at an early stage in this process and the governments then go away and work with parties in the North and so on to develop detailed plans."

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Dr Renwick also said that there would have to be a referendum in Ireland on any constitutional amendments. "But if the South is getting to vote at the end of the process, is it really tenable for the North not to get to vote at the end too?" he asked.

Sinn Fein deputy leader Michelle O'Neill welcomed the study.

"This is further proof that focus is now shifting to constitutional conversations about how our island is shared in the future, particularly given the threat of the North being dragged out of the EU against its expressed wishes," she said.

"Existing constitutional principles exist in both jurisdictions which will guide the process.

"We welcome the academic study which will examine this, but that work has yet to be concluded.

"The conversation about Irish unity is live and centre stage. We need to have as broad and comprehensive a debate about the future as possible and convince the greatest number of people of the merits of Irish unity."

The academic group is expected to produce a report by autumn next year, but the DUP reiterated that any talk of Irish unity was "divisive".

"A border poll would take this community backwards. Our focus should be on restoring devolution and ensuring people here have all the services they require," it said.

An Alliance Party spokesperson added: "We are clear that whatever the constitutional position, the priority must be to promote reconciliation and to make this region work.

"Nevertheless, without prejudice to any future decisions, it is helpful for rational exploration of the mechanisms and practical issues involved in any future change."

Belfast Telegraph