NORTH Down MP Lady Sylvia Hermon has called on the secretary of state to clarify how a Brexit would affect border security.
The independent MP said Theresa Villiers, who supports a Brexit, has a responsibility to explain "precisely what is going to happen to the border".
She questioned how the PSNI could police the border.
"I want to know from our secretary of state what she anticipates are going to be the arrangements along the border with the Republic of Ireland in the event of the UK voting to come out of the EU," she said.
In response, Ms Villiers insisted a Brexit would not lead to strict security along the border.
"It really is a scare story to say that suddenly we are going to have Troubles-style security checks and towers around the border," she told the BBC.
"It is not going to happen. We can keep an open border with the Republic of Ireland."
On Thursday, two former prime ministers - Sir John Major and Tony Blair - visited Derry to warn that a vote to leave the European Union would undermine the peace process.
"We understand that, although today Northern Ireland is more stable and more prosperous than ever, that stability is poised on carefully constructed foundations," Mr Blair said. "And so we are naturally concerned at the prospect of anything that could put those foundations at risk."
However First Minister Arlene Foster, who is in favour of leaving the EU, criticised Mr Blair and Sir John.
"I do find it rather disgraceful for two prime ministers, who know full well the importance of the peace process here in Northern Ireland, to come over here and suggest that a vote in a particular direction is going to undermine that, is quite scandalous," she said.
