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[CARLINGFORD, Ireland] Businesses on both sides of the open border that divides Ireland are watching Britain's EU referendum with a wary eye, concerned that a bygone era of customs checks could return.
On the Republic of Ireland side, adventure centre owner Tom McArdle fears he could lose customers who zigzag across the frontier every day if Britons vote to leave the European Union on June 23.
Mr McArdle, 70, has operated his business for 26 years - long enough to recall the tedious paperwork inherent in cross-border orders and to have experienced the delays at the crossing points.
"It's the unknown that worries us," he said at his centre, only a kilometre as the crow flies from the border that bisects Carlingford Lough, a scenic stretch of water where he organises kayaking and sailing.
His business attracts up to 400 visitors a day, many of them from Northern Ireland - 10km away by road.
"The biggest single worry is a return to border restrictions. We have a lot of groups coming here from Northern Ireland and the prospect of delays at the border might well discourage them," he said.
Mr McArdle is not alone.
Farther up the lake in Omeath, Joe Morgan has employees from both countries at his seafood processing plant and supplies supermarkets, hotels and restaurants across the region.
"It would be a nuisance every day," he said.
Ireland has the euro while Northern Ireland uses the pound and the two sides have different tax rates, but the physical border has only simple road signs alongside crumbling former customs buildings.
The barriers were abolished on January 1, 1993.
In the event of Brexit, the 500km stretch would become the sole land border between the United Kingdom and the European Union.
"It is inevitable that border controls would have to return - the whole Brexit argument is around this very point," former Northern Ireland police chief Hugh Orde wrote in a letter to the Irish Times.
"If you shut the front door, leaving the back door open would be stupid," he said.
"Leave" campaigners argue that these fears are overblown, as existing bilateral agreements between Britain and Ireland would remain in place.
"There would be risks to manage but they are not significantly more serious than risks that are already managed effectively today through bilateral co-operation," Northern Ireland minister Theresa Villiers, who backs a "Leave" vote, said on Thursday.
Her assertion offers little reassurance for many people in a cross-border region which is still only taking faltering steps towards recovery, after three decades of armed conflict in Northern Ireland that stymied growth and killed some 3,500 people.
Brussels has injected billions of euros into Northern Ireland to aid economic and social recovery after the 1998 Good Friday Agreement signed in Belfast brought a measure of peace to the blighted region.
And with 34 per cent of Northern Irish exports going to the Irish republic, it also stands to lose more than the rest of Britain in the event of a Brexit.
A study by the global ratings agency Standard & Poor's earlier this week placed Ireland among the countries that would be hardest hit by Brexit.
Unlike national opinion polls that are running neck-and-neck, polls in Northern Ireland consistently deliver a large majority for staying in the EU.
Nationalists, many of whom regard Brussels as a counterweight to British rule from Westminster, are the most ardent supporters of the status quo.
Unionists are more divided - the majority express a desire to leave, citing a desire to regain British sovereignty, but a significant minority who are campaigning to remain, largely for economic reasons.
Michael McKeown, head of the Newry Chamber of Commerce in Northern Ireland, said his members overwhelmingly supported "Remain", regardless of religious affiliation or national identity.
"This vote boils down to a single issue: whether or not we have a hard border.
"We have a collective strong living memory of what a hard border looks like and entails.
"If there is even a chance of a hard border being re-introduced, then it is a chance we cannot afford to take."