A vote to quit the EU would not mean the end of free travel across the Irish border, Secretary of State Theresa Villiers has insisted.
Ms Villiers, a strong advocate for Britain quitting the EU, also denounced the suggestion that leaving the EU could undermine the peace process as "scaremongering".
Ms Villiers said Ireland's Ambassador in London, Dan Mulhall, had refused to endorse the idea that a Brexit could hurt the peace process in evidence he gave to Westminster's Northern Ireland affairs committee.
In her first major speech on the June 23 EU referendum, Ms Villiers said the Common Travel Area between the UK and Irish Republic would out-last the EU. The unique status of Irish citizens in Britain would also continue, she added.
Earlier this week, Lord Lawson suggested that checkpoints would be needed on the border if the UK pulled out. The Conservative former chancellor said a Brexit would result in the introduction of controls along the 310-mile frontier.
But Ms Villiers replied: "If we vote Leave, we would be entitled to remove people who have entered the UK through our common border with Ireland if they are not entitled to be here. We had a Common Travel Area with Ireland before we joined the EU and we will have one after we vote to leave. There would be no need to erect border controls."
Irish Foreign Affairs Minister Charlie Flanagan said he knew Ms Villiers opposed Britain's EU membership. But he added that the Irish government wanted Britain to stay in the EU, which continues to support peace and prosperity in Northern Ireland with generous funds.
"North-south co-operation is far easier when both jurisdictions are within the EU," Mr Flanagan said.
At the same time the British Ambassador in Dublin, Dominick Chilcott, urged the 130,000 British people living in Ireland to register for a vote in the referendum.
And Ryanair boss Michael O'Leary appealed to Irish people living in Britain to mobilise in favour of EU membership. He said he believed most British people favoured EU membership but the referendum could be a mid-term backlash against David Cameron.