A referendum on unifying the Republic of Ireland and Northern Ireland will happen within the next six years, according to the president of Sinn Fein.

Mary Lou McDonald was speaking to Sky News following the restoration of the Northern Ireland executive, where her party – a nationalist group – is now the largest caucus in Belfast for the first time since the Good Friday Agreement came into effect.

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She said: “What I firmly believe is – in this decade – we will have those referendums, and it’s my job and the job of people like me who believe in reunification to convince, to win hearts and minds and to convince people of that opportunity – part of which, by the way, will be really consolidating our relationship with Britain as our next door neighbour and good friend.”

Asked if she meant before 2030, Ms McDonald said “yes”.

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Under the terms of the Good Friday Agreement, there is a pathway for a reunification poll to be held in Northern Ireland.

The legislation states that “if at any time it appears likely” that a “majority of those voting would express a wish that Northern Ireland should cease to be part of the United Kingdom and form part of a united Ireland”, then the Northern Ireland secretary will order a vote.

How the majority would be demonstrated is less clear.

According to the Institute For Government, there is no parallel mechanism in the Good Friday Agreement for a referendum in the Republic of Ireland, where Ms McDonald is a politician.

But it sets out that at least two referendums would need to be held – one on the principle of reunification, and then one to amend the constitution if Northern Ireland agrees to join the Republic of Ireland following negotiations.

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Fairly realistic to predict unity referendum

David Blevins

Senior Ireland correspondent

@skydavidblevins

When it comes to the question of referendums, it’s worth considering alongside the most recent polling.

A decisive 64% of people in the Republic of Ireland are in favour of Irish unity.

In Northern Ireland, it’s not so clear-cut – only 30% in favour, 50% against and 20% undecided.

But there are two key factors – the most recent Ipsos poll in the Irish Times last December suggested the number of unionists in Northern Ireland who say they would not be able to accept Irish unity has fallen from 32% to 23%. That’s very significant.

And then – believe it or not – 60% of people in Northern Ireland, unionist and nationalist, believe there should be a referendum in the next ten years.

So we think what Mary Lou McDonald is predicting is fairly realistic – that a vote will take place in the next decade.

What is less predictable is what the outcome of that vote will be.

Asked about her previous comments that unity is within touching distance, the Sinn Fein president said she was talking in “historic terms”.

“I don’t mean that it’s happening next week or next month,” she added.

Speaking about her prediction for the next six years, Ms McDonald said: “Yes and let me say that is not so far away – so there’s an awful lot of work that needs to be done.

“I’ve said consistently to the government in Dublin that they really need to take possession of this conversation that’s now under way right across Ireland.

“They need to give it a structure and a place and of course it has to be inclusive – we want to hear from every voice, including those for whom reunification would not be their first option – those who go out and campaign for the union.”

But Ms McDonald added: “Nevertheless, we all live together, that’s never going to change. We share Ireland.

“We love Ireland, and we want what’s best for our children, for our grandchildren. I think that’s the strongest, most powerful common ground that we all share.”