EU exit is bad for Northern Ireland cross-border trade: Treasury
Northern Ireland's cross-border business with the Republic would be hampered by customs controls if the UK leaves the EU, the Government has warned.
A report from the Treasury has examined the long-term impacts of a Brexit.
And Chancellor George Osborne says the UK will be permanently poorer if it votes to leave the EU, with households £4,300 a year worse off.
The report also highlights that Northern Ireland receives more from the EU than other regions in the UK.
And it says that given more than a third of Northern Ireland's trade in goods and services is with the Republic, leaving the EU "would affect the current high level of cross-border activity and trade flows".
"Outside the customs union, goods being exported across the border could be subject to various forms of customs controls, and their liability to duty determined according to complex rules of origin," the report added.
"The latest data shows 37% (£3.6bn) of Northern Ireland's goods and services exports go to Ireland."
The report said that in 2014, the province's manufacturing sales to the Republic were worth £1.4bn - accounting for 10% of its total external manufacturing sales and the equivalent of 37% of its domestic sales.
Mr Osborne warned that the poorest would suffer most from the economic shock of Brexit.
But DUP MP Sammy Wilson has said the Government is "resorting to ever increasingly desperate tactics".
"The latest is these dire predictions about the economic consequences of leaving the EU," he said.
"To suggest that any economic model can predict what our economy let alone the EU and world economy will look like in 14 years' time is totally dishonest."
Meanwhile, another report has claimed Northern Ireland would be worst hit by a Brexit than any other UK region, with decades of cross-border trade placed at risk.
But the report from Davy Private Clients also said Northern Ireland could be handed more powers from Westminster if the UK leaves the EU.
Davy Private Clients said: "While the UK is a net contributor to the EU, Northern Ireland as a region is a net beneficiary.
"Most importantly, Northern Ireland is the only part of the UK which shares a border with another EU member country."
And it says it "has taken decades to reach the current fluid movement of trade and people and to open exchange of economic, cultural and political life across this border".
The report points to Northern Ireland's level of trade with the Republic and also says farming and agri-business will be "most at risk" from a Brexit.
"Most at risk is the agricultural sector, of which 82% operates under the EU's Common Agricultural Policy and which is due to receive an estimated €3bn (£2.4bn) in EU aid for the period 2014-2020."
But aside from a financial impact, the report from Davy also says that there is a "very strong possibility that, following a vote to leave the EU, the UK would need to seek constitutional settlements with Northern Ireland and Scotland".