By Andrew MacAskill
LONDON (Reuters) - Britain's opposition Labour leader Jeremy Corbyn has unveiled a leaked government document which shows the damaging impact of Prime Minister Boris Johnson's Brexit deal on Northern Ireland's economy, saying it is evidence he is misleading the public.
Johnson has repeatedly said there would be no customs checks on goods moving between Northern Ireland and mainland Britain under the divorce deal which he agreed with the European Union.
But the document, marked "official, sensitive", says exporters would have to make customs declarations when moving goods between Northern Ireland and Britain and these new barriers will be "highly disruptive" to Northern Ireland's economy.
The leaked analysis warns that 98% of Northern Irish exporters to Britain are small to medium sized businesses, which are "likely to struggle to bear" the cost of new border checks.
"This is the cold, hard evidence that categorically shows the impact Johnson's damaging Brexit deal will have on large parts of our country," Corbyn said in a speech in London.
Under Johnson's divorce deal, Northern Ireland would remain aligned with the EU's single market rules for trade in animal, food and manufactured goods to resolve the biggest sticking point in negotiations: how to ensure there is a seamless border between Northern Ireland and Ireland.
The 500-km (300-mile) border will be the United Kingdom’s only land frontier with the EU after it leaves the bloc. The government has agreed to the arrangements for Northern Ireland to avoid erecting checkpoints that could undermine a peace deal, which ended decades of conflict in the province.
Johnson said in response to Labour's claims that there would be no custom checks on goods traveling between Britain and Northern Ireland. He said he had not seen the leaked document but described it as "nonsense".
A senior government source said the document was written by a junior government official, which was not formally approved.
The Conservative Party later said that businesses which export from Britain to Northern Ireland will face some customs checks, contradicting the prime minister's claims.
Last month, Johnson told Northern Irish businesses they would not encounter additional paperwork when trading with Britain and they can put customs declarations forms in the bin.
The leaked document, however, says: "At minimum, exit summary declarations will be required when goods are exported from Northern Ireland to Great Britain."
The document states that new barriers could lead to higher prices in the province and that unemployment in areas like retail is likely to rise.
Labour's Brexit plan is to negotiate a new deal with the European Union to include a customs union and then hold another referendum on whether to accept it, although Corbyn himself has vowed to remain neutral.
This is the second time Corbyn has held a press conference to make public internal government documents. Last month he showed what he said was evidence that the state-run health service -- much loved in Britain -- was being discussed in trade talks with the United States.