A British withdrawal from the European Union would play into the hands of criminals, right-wing extremists and Vladimir Putin, former Irish premier John Bruton has warned.
The ex-EU ambassador also said there was little talk in London about the impact of a Brexit on regions outside the capital dependent on manufacturing jobs which would be worst hit by new trade tariffs.
Appealing to voters in Northern Ireland ahead of an in/out referendum, Mr Bruton said the consequences of a withdrawal are “unknowable” but likely “quite dramatic”.
“A disunited Europe, of 28 or more separate countries, pursuing their own agendas would become a playground for outsiders seeking advantage and playing one off against the other,” he said.
“(Russian president) Vladimir Putin would be happy.”
Mr Bruton said a UK opt-out would “most certainly” weaken the EU and the precedent would be seized upon by far-right leaders, including France’s Marine Le Pen and Geert Wilders in the Netherlands, to redraw boundaries.
“All over the world, those who do business with the EU would begin to wonder.... is the EU going to break up? Are others going to follow the UK out the door?” he said.
“Europe’s borders could again become barriers behind which criminals could hide.”
The ex-taoiseach said he was surprised at the lack of thought given in London to the impact of a Brexit on UK regions, particularly Northern Ireland and Scotland, as well as to the future of the UK itself.
Along the Irish border, customs posts would have to re-erected and, if immigration controls were to be imposed, passport checkpoints would have to be set up for the first time in history.
“That would disrupt lives, and it would disrupt business,” he told the annual dinner of the Council of the Incorporated Law Society of Northern Ireland, in the Ulster Museum.
“Many firms process raw materials originating in the Republic (of Ireland) here, and vice versa.
“All that would have to be subject to customs inspection, a costly and intrusive process.”
He added: “Smuggling would undergo a revival, with endless profit making opportunities opened up for subversives and organised criminals.”
Mr Bruton said if EU tariffs were to be imposed on UK exports as a result of a Brexit, the North East of England, with its big manufacturing base, would lose the most.
Northern Ireland and the East Midlands would be next hardest hit - while London, with many of its jobs unaffected by trade tariffs, stood little to lose.
“Northern Ireland would lose almost twice as much as Wales would,” he added.
Farmers, he warned, should think whether the UK Government would or could plug a multi-billion pound hole in EU funds and subsidies sent to Northern Ireland from Brussels.
“In a world in which Europe is becoming a smaller force, economically, politically and in population, a weakened EU would probably not be in the interests of Europeans, whether they live in Belfast or Bratislava, in Downpatrick or in Dubrovnik,” he said.
Mr Bruton was EU Ambassador to Washington from 2004 to 2009.