Border controls could have to be set up between the Irish Republic and Northern Ireland in the event of a Brexit vote.
Irish Taoiseach Enda Kenny issued the warning as he called on Irish people living in Britain to vote remain next month. The Irish leader, speaking in London, said Irish people make up a “substantial” part of the electorate and urged them to use their vote. Irish citizens living in the UK will have a vote on 23 June, alongside British citizens who are living in Ireland.
Campaign Group Irish4Europe estimates there are around half a million first generation Irish living in England, Scotland and Wales.
Mr Kenny said: “We would say, with particular reference to the Irish people living in Britain, this is a really important decision. Its outcome would affect people in Northern Ireland, it would affect Ireland itself and obviously will have an impact upon the European Union for many years to come.”
Asked what might happen in the event of a vote for Britain to leave the EU he said there would have to be “significant, complex and difficult negotiations”.
He added: “Ireland in Europe would still stand by Britain being a member of the Union and of its importance but I have no idea what other European countries, how they would look at Britain whether they decide to leave, given the fact that we’ve come a long way since the 1970s.
“So whether there would be border controls or custom controls, these things are a possibility but obviously they would require some very serious negotiations and my preference for the Irish electorate who have a significant part in this referendum is to vote to stay, for Britain to stay as a strong and central member of the European Union.”