DECADES of cross-border policing co-operation will "fall away" after a no-deal Brexit, the Republic's police chief has warned.
Garda Commissioner Drew Harris said his officers would work with their northern counterparts to mitigate the impact of a disruptive Brexit but said there was "concern" that EU criminal justice treaties would no longer apply.
The former PSNI deputy chief constable said the cross-border sharing of information and joint operations would continue.
"I know the chief constable of the PSNI and myself are not going to sit idly by and allow a threat to just develop," he said.
His comments came as Stormont's pro-Remain parties warned European Council President Donald Tusk of "grave concerns" over the increased likelihood of the UK crashing out of the EU.
An open letter signed by Sinn Féin's Michelle O'Neill, Alliance's Naomi Long, the SDLP's Colum Eastwood, and the Green's Clare Bailey, highlights the risk to thousands of jobs and disruption to cross-border trade.
"It is our view that the progress made in developing integrated and enduring relationships on this island, politically, economically and socially, over the last 20 years is far too important to abandon," the letter said.
DUP MP Sir Jeffrey Donaldson said the letter demonstrated that the backstop does not have the cross-community support.
