Northern Ireland Secretary Theresa Villiers has rejected suggestions that UK withdrawal from the EU would require border checks to be reinstated with the Republic of Ireland.
Ms Villiers, who is campaigning for Brexit, said there was "every reason to suggest" that the UK and Ireland could maintain free movement under the kind of common travel area arrangement which existed before the two countries joined the EU in 1973.
She dismissed calls for her to step down from her Cabinet position while campaigning for a Leave vote, telling BBC Radio 4's World at One: "I think it's perfectly reasonable for me to have chosen a side in this referendum. The great thing is that every single person in the UK, including in Northern Ireland, will get to take this decision, not just the Secretary of State."
Asked whether Brexit would mean tighter border controls with the Republic of Ireland, Ms Villiers said: "That's not inevitable at all. We've always had a much closer relationship with the citizens of the Republic of Ireland than with the rest of the EU.
"It's perfectly possible to maintain that free movement with Irish citizens. After all we give them privileges in the UK which we accord to no other EU citizens, like the right to vote in our elections."
It was "certainly not impossible" to manage the risk of migrants from third countries crossing into the UK from Ireland, she insisted.
And she added: "I don't think anyone should assume that border checks should be introduced as a result of a UK exit.
"We are in the area of scare stories. We do need to recognise that the relationship between the UK and Ireland when it comes to this common travel area is decades older than our EU membership and doesn't depend on it.
"We've run an effective common travel area for many decades with the Republic of Ireland and there's every reason to suggest that that would continue whether we leave the EU or we don't. It's manifestly in our interests to ensure that ease of passage across the border between North and South is as easy as possible. No-one is wanting to wind the clock back and to introduce the kind of security checks at the border that there were during the Troubles."
Ms Villiers played down the risk that companies would relocate to the Republic of Ireland in order to remain in the EU, insisting the North will remain an "immensely competitive" place to do business.
"I think Northern Ireland would still be immensely competitive outside the EU," she said.
"It has a phenomenally successful manufacturing base. It has companies that are selling all round the world. And there are many large global companies that have made it absolutely clear that they would continue to invest in the UK if we withdraw from the EU, and they wouldn't face the same costs that come with the European Union at the moment."