Colum Eastwood has welcomed confirmation from Brexit Secretary David Davis that Northern Ireland would have an "automatic route" back into the EU if it were part of a united Ireland.
Unlike Scotland, which has been told it could be forced to join a queue for membership of the bloc if the country votes for independence, the province would not have to reapply for EU membership, as the Republic is already one of the existing member states, Tory minister said.
In a letter to SDLP MP Mark Durkan, David Davis wrote: “If a majority of the people of Northern Ireland were ever to vote to become part of a united Ireland the UK Government will honour its commitment to enable that to happen.”
He added: “In that event, Northern Ireland would be in a position of becoming part of an existing EU member state, rather than seeking to join the EU as a new independent state.
"It would of course be for the EU Commission to respond to any specific questions about the procedural requirements for that to happen."
Mr Davis stressed that the UK Government was committed to the current constitutional settlement with Northern Ireland remaining "a strong member of the United Kingdom with strong North-South and British-Irish relationships".
Brexit has shaken the tectonic plates of our constitutional landscape. Colum Eastwood
SDLP leader Colum Eastwood said: “In successive referenda, the people of Ireland have voted for a constitutional settlement in the north based on common membership of the European Union across this island. That was the basis of securing the consent and confidence of nationalism for the Good Friday Agreement.
“The current British Government’s Brexit juggernaut threatens to smash through the fragile complexities of the Irish political dispensation.
“Over the course of the last number of weeks, SDLP MPs and negotiators have pressed the British Government to concede that unlike any other part of these islands, we have an automatic route back into the European Union. The principle of consent and provisions for a unity referendum in the Good Friday Agreement allow people here to make the decision to join a sovereign united Ireland and, in doing so, rejoin the European Union.
“It is welcome that the Brexit Secretary has now conceded that argument.
“Brexit has shaken the tectonic plates of our constitutional landscape. People in Northern Ireland voted to remain in the EU. The people of Ireland voted for the Good Friday Agreement underpinned by Europe. If that context is to be ripped apart and our political foundations thrown into flux, then the time will be right for people here to begin to explore our constitutional future.”