Frictionless trade between Northern Ireland and the rest of the UK would be maintained under the proposed Brexit deal, the Prime Minister has said.
Boris Johnson visited a crisp manufacturer in Co Armagh on Thursday and took a turn on the production line.
His proposed EU deal foundered after DUP opposition to what some unionists have termed a border in the Irish Sea.
An elaborate system involving the imposition of tariffs on goods going into the Republic of Ireland via Northern Ireland is designed to maintain an open land border on the island.
Mr Johnson said: “This is a wonderful thing for NI because it allows the whole of the UK to leave while making sure there is not any border at all between Northern Ireland and the south, but also, and this is a very important point to get across, no friction at all west-east or east-west.
“There has been a lot of misunderstanding about the deal and perhaps one of the things that I wish we could have spent a bit more time explaining it because there won’t be any checks on stuff coming from Northern Ireland to Great Britain, we won’t be implementing, we are the Government of the UK, we won’t be implementing any checks, of course not.”
He claimed Labour leader Jeremy Corbyn would offer an “appalling” threat to the union with Northern Ireland.
Mr Corbyn held meetings with Sinn Fein leaders decades ago during the conflict.
The Prime Minister also criticised his rival over the possibility of referenda on Scottish independence and EU withdrawal.
He said: “Another turgid, torpid, toxic appalling EU referendum, which is the last thing we need.”
He said tariffs levied on goods coming from Great Britain and going on to the Republic would represent a very small minority.
“If people don’t like it they can vote it out in four years’ time.”
Mr Johnson visited the Tayto crisp factory in Tandragee and said he would be keeping some at Downing Street, admitting he tried the cheese and onion.