A return to a hard border in Ireland after Brexit would be a "very unhealthy development", a former director of GCHQ has warned.
A rise in smuggling which would benefit paramilitaries and a hit to community relations would be a result of a return to solid infrastructure between the province and Ireland, according to Robert Hannigan, who led the British intelligence agency from 2014 to 2017.
The Irish border is one of the key sticking points in Brexit negotiations, with both the British government and the EU stressing they want to avoid it.
He told BBC Radio 4's Today that a hard border would "fray around the edges of the peace process".
He continued: "It wouldn't suddenly bring a return to the conflict I don't think.
"But it would lead to poorer community relations and it would certainly lead to a rise in smuggling and historically, right through the troubles, smuggling was bad for peace because it meant a lot of money going to criminal groups who were closely allied with or became paramilitary groups.
"So it's a very unhealthy development."
