The UK will not become a safe haven for terrorists and international organised crime gangs in the event of Brexit, Northern Ireland's top police officer has said.
PSNI Chief Constable George Hamilton told MPs that if the UK splits from the EU new bilateral agreements would have to replace existing treaties on data sharing, extradition and investigations.
He said new arrangements would be more expensive, clunky and not as slick as the current systems.
"Some of the public commentary from within the broader policing community around the UK becoming a safe haven for organised criminals and terrorism and all the rest of it personally is not my position," the Chief Constable said.
Mr Hamilton told the Northern Ireland Affairs Committee the transition to new cross-border policing would take two years.
The MPs were told new international justice agreements would have to involve rules on joint investigations to allow domestic laws to be used in a host country and a replacement European Arrest Warrant system for extradition.
They also heard agreements on sharing DNA records, fingerprints, biometric data and vehicle registrations of suspects and co-operation against terrorism under the Prum convention would also need to be rewritten.
The Chief Constable cited the example of bilateral treaties signed by Switzerland and Norway with EU states and the PSNI's good working relationship with US police and justice chiefs.
"I think all of this is probably doable with an exit but it would be slower, complicated and more costly ... from a practical policing perspective," Mr Hamilton said.
PSNI Assistant Chief Constable Will Kerr told the MPs that p hysical borders are becoming less of an issue for policing international organised crime and that the increasing threat to security and law and order is online.
"The borders tend to be less and less relevant now," he said.
"Organised crime gangs can operate largely with impunity I have to say in China or Eastern Europe or in the Ivory Coast and can very effectively, with almost call centre organisation, extort and bribe, particularly around sexual impropriety in many other parts of the world."
The Irish border is 224 miles long with 292 crossing points and the committee was told there is "more or less unfettered access" into Northern Ireland from the Republic.
The officers said there is some evidence of illegal immigrants moving from the Republic to Northern Ireland and human trafficking but not on the scale it has been portrayed in some quarters. The PSNI put the figure as less than hundreds.
"The old style of border security ... how effective they actually were in monitoring movement across the border and stopping terrorist attacks and so on, they actually became more of a target for attacks," the Chief Constable said.
"Whatever model in the event of an exit we come up with we would like to be giving a view, an operational policing perspective, that would be much more intelligent than simply building walls and sangars and crossing points."
The Chief Constable declined to criticise retired police chiefs who have spoken out on the Brexit debate, adding: "I'll not talk about other people, I'll talk about myself - seven years after I leave office the only place I will be commenting is TripAdvisor."
The committee, which is examining the potential impact of a split from the EU on Northern Ireland, including relations with the Republic, also took hours of opinions from business figures at Stormont.