The leaked document was revealed today by British Labour Party leader Jeremy Corbyn.
He said: “The Treasury analysis revealed by the Labour Party today is unambiguous.
“It lays out in clear terms that the vast majority of exporting businesses in Northern Ireland will struggle to bear the costs of a new customs declaration and regulatory check regime under Boris Johnson.
“This adds further weight to our argument that there is no good Brexit, there are only degrees of economic self harm.
“The only way to protect people, businesses and communities here is to stop Brexit and stop Boris Johnson.
“The alternative is economic devastation, rising prices for consumers and rising unemployment. No one here voted for that future and it’s not something we should be subjected to.
“The SDLP is being honest with people.
“We oppose Brexit and we’ll do everything in our power to stop it.
“We’ll go to Westminster to use our influence and our votes as part of a progressive coalition to bring an end to this chaos and an end to Boris Johnson’s administration.”