BORIS Johnson has been accused of not understanding his own Brexit deal after he told Northern Ireland businesses they can put customs declarations forms “in the bin” because there will be “no barriers of any kind” to trade crossing the Irish Sea.

The Prime Minister has suggested Brexit Secretary Stephen Barclay had been wrong to say goods between Northern Ireland and the rest of the UK would face checks as a result of the Brexit deal struck with the European Union.

Barclay previously told MPs that “some information” and “minimal targeted interventions” would be required on goods travelling between the two areas of the UK, due to Northern Ireland remaining aligned with EU trading rules for agricultural products and manufactured items as part of the exit terms.

But in a personal intervention, the PM told Conservative supporters and Northern Ireland business figures the Secretary of State’s advice was not correct.

The Tory leader, in a video shared by Manufacturing NI on Twitter, said there would be “no forms, no checks, no barriers of any kind” as a result of his Withdrawal Agreement.

Johnson was asked by Irwin Armstrong, owner of Ciga Healthcare, whether he could “go back to my company in the morning and tell my staff we will not be filling in any customs declarations for good leaving Northern Ireland to go to GB?”

The PM replied: “You can.”

He added: “If somebody asks you to do that, tell them to ring up the Prime Minister and I will direct them to throw that form in the bin.

“You’ll be alright,” Johnson assured. “There will be no forms, no checks, no barriers of any kind. You will have unfettered access.”

Jonathan Portes, a professor of economics and public policy at King’s College, London, said Johnson’s remarks showed he did not understand his own Brexit deal.

He tweeted: “Seems entirely clear that the Prime Minister does not understand his own Brexit proposal (for a hard border in the Irish Sea) *at all*.”

Anna Jerzewska, a customs expert, pointed out customs controls were in the Brexit deal to facilitate the international trade agreements Johnson wants while keeping the Irish border open.

She tweeted: “If we want to sign trade deals our trade partners will want to know which goods come from NI and which from ROI [Republic of Ireland] and we need to find a way to collect this info.

“EU FTA partners will want to ensure goods come from the EU and not GB.”

Johnson added to his remarks yesterday saying: “We’re the UK. We will not be instituting such checks.”