Jeremy Corbyn has insisted he is not asking for or advocating a referendum on Irish unity, as he addressed the issue during his first visit to Northern Ireland as Labour leader.
Mr Corbyn fielded questions from students at Queen’s University, Belfast a day after his official spokesman said he believed there was majority support for unification across the island of Ireland.
The Labour leader has, in the past, made no secret of his support for a united Ireland.
However, he said on Thursday that, if he was to become prime minister, he would only trigger a border poll in line with the terms of the Good Friday Agreement.
A border poll - which would see separate votes in Northern Ireland and the Republic - can only be called if the UK Government believes a majority within Northern Ireland is in favour of unity.
“If that is a wish, then clearly such a poll would happen,” Mr Corbyn said, in response to a question on the subject from a Queen’s University politics student.
“I am not asking for it, I am not advocating it.
“What I am asking for is a return to the fullness of the Good Friday Agreement which would open up the opportunity and possibility for the future of Ireland as a whole.”
Mr Corbyn added: “That is the point of the Good Friday Agreement.
“Not direct rule, not imposition of a political view from Westminster, but devolution of powers to Stormont here and of course the relationship with the Republic.”
“It’s quite clear that it’s there for a poll on both sides of the border, should that be something that is demanded.”
Earlier, Mr Corbyn warned that Northern Ireland stood at a potential crossroads between a strengthened peace and a return to the dark days of the past.
He urged Stormont leaders and the UK and Irish Governments to renew efforts to restore power-sharing at the crisis-hit institutions in Belfast, insisting peace cannot be taken for granted.
“I want to make a plea to all parties and all sides. We must do all we can to make power-sharing work again in Stormont,” he said.
“We need all sides to come together and make devolution work again.
“That means tough choices. It means compromise and give and take.
“But we owe it to the people of these islands not to allow political disagreements to open the way for any return to the grim days of the past.”
Northern Ireland has been without a properly functioning power-sharing government for more than 16 months due to a bitter stand-off between the two biggest parties, the DUP and Sinn Féin.
Mr Corbyn also called on Prime Minister Theresa May to reconvene the British Irish Intergovernmental Conference - a body that offers the Irish a consultative role in non-devolved matters concerning Northern Ireland.
Sinn Féin and the SDLP have been demanding the re-establishment of the conference, which last sat in 2007, as a means to plot a way forward amid the devolution crisis in Belfast.
However, unionists are wary of the body, and associated suggestions that the Irish Government could have a significant role in deciding the next steps for the region’s rudderless public services.
DUP leader Arlene Foster has dismissed the conference as a “talking shop” and instead called for direct rule UK ministers to take decisions on Northern Ireland at Westminster until such time as a power-sharing administration can be pieced back together at Stormont.
Mr Corbyn, who is spending two days in Northern Ireland, also used his speech at Queen’s to make clear that Labour will not support a Brexit deal which results in the re-imposition of a hard border.
He argued that the best way to avoid border checks is through a UK-EU customs union - which would offer the UK a say on future trade deals - coupled with a “new and strong relationship” with the EU single market.
“Driven by the free-market fantasists within their ranks, the reckless Conservative approach to Brexit is a very real threat to jobs and living standards here in Northern Ireland and risks undermining and destabilising the co-operation and relative harmony of recent years,” Mr Corbyn, who will visit the border on Friday, said.
“Labour will not support any Brexit deal that includes the return of a hard border to this island. But we are also clear there must be no border created in the Irish Sea either.”
The Labour leader added: “Opposition to the idea of bringing back a hard border to this land isn’t just about avoiding paperwork or tariffs - important though that is – it’s about deep rooted cultural and community ties.
“An open border is a symbol of peace, two communities living and working together after years of conflict, communities who no longer feel that their traditions are under threat.”