“Although the existence of the common travel area could still allow for free movement of people, this is by no means certain in the event of success for the Brexit campaign,” he said.
“Despite the noise to the contrary coming from the leave camp, including the DUP, it’s clear there would have to be some form of customs posts between the UK and the EU, in particular on the Irish border.
“Leaving the EU will result in a significant change in relationship between the Republic of Ireland and the UK which we cannot ignore.”