A vote for Brexit would endanger the union of the UK, with uncertainty surrounding the country's border with Ireland, according to Remain campaigner Amber Rudd.
Vote Leave admit that they "don't know" what would happen to the UK border with Ireland.
Fact-checking organisation Full Fact say that "don't know" is a fair summary.
Nobody can be sure what would happen to borders between the Republic of Ireland and the UK if we vote to leave the EU. Claims that there would or wouldn’t be border controls on the island of Ireland are predictions, not facts, at this stage.
Some sort of customs checks on goods crossing the border would be needed, but not necessarily passport checks or stopping everyone.
It depends whether the a post-Brexit UK puts restrictions on EU immigration.
Campaigners for remaining in and leaving the EU have clashed in a fiery debate on ITV.
On a night of fierce debate between Remain and Leave campaigners during the ITV referendum debate, which of the claims actually stacked up?
Analysis of ITV's EU referendum debate.