Conservative politicians have warned of free movement being disrupted if the UK goes...
Former British chancellor Nigel Lawson has warned that border patrols could be put back in place if the UK decides to leave the EU in June.
Mr Lawson said that "there would have to be border controls" between the Republic of Ireland and Northern Ireland if Britain leaves.
This would not block "genuine Irish from coming in, from crossing the border," rather it would stop a potential weak spot forming between the EU and the UK according to the former politician.
"There is now particularly close co-operation between the security services in Northern Ireland and the security services in the Republic to prevent the IRA and the terrorist threat from being worse than it is," he continued.
Tory MP Dominic Raab also said there will need to be some "form of checks" if the UK leaves the EU.
“If you are worried about border controls and security.... if you are worried about the effect of those EU rules, then you couldn’t leave a back door without some kind either of checks there with any country or assurances in relation to the checks that they are conducting, obviously, otherwise everyone with ill will towards this country would go round that route,” the 'pro-leave' MP told Sky news.
"So the truth is that the broader point here is that if you want to have safe borders if we want to have proper checks to deal with terrorism and broader crime, you have to come out of the EU," he continued.
However research from Open Europe, a pro-Europe group says that there is "no reason why the UK and Ireland could not retain the Common Travel Area and so avoid the need to introduce passport controls, which would enable the continued free movement of people between the UK and Ireland."
Secretary of State for Northern Ireland Theresa Villiers has previously said that there is "every reason to suggest" that free movement between Ireland and the UK will be retained if the UK goes.
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," the conservative MP said.