Prime Minister accused by Labour of being ‘caught lying’ over Irish Sea barriers to trade after leaked document contradicts him

In yet another blow to the prime minister’s trustworthiness, the Treasury document yet again contradicts Mr Johnson’s claim that his deal will not involve the erection of an Irish Sea border.

Trade experts, business groups, some of Mr Johnson’s ministers and his own government’s document explaining his deal make clear that it will involve additional burdens on goods travelling from Northern Ireland to Great Britain and vice versa.

But yesterday Labour leader Jeremy Corbyn revealed a leaked Treasury analysis of his proposed deal – which he attempted to rush through the Commons with minimal scrutiny before calling the election.

Mr Johnson has made clear that he will attempt to get MPs to pass his “oven ready” deal soon after the election.

Yesterday Mr Corbyn, whose manifesto rules out even a regulatory border in the Irish Sea, said that the confidential document “drives a coach and horses” through Mr Johnson’s claims and further exposes the prime minister for “deliberately misleading” the public.

The Labour leader brandished the dossier marked “official – sensitive” at a press conference on Friday, saying it is “cold, hard evidence” from the Treasury that the PM’s Brexit deal would damage the nation.

The report sets out the belief that there will be customs checks between Great Britain and Northern Ireland after Brexit, something Mr Johnson has claimed would not happen.

The Tories said the documents did not back up Mr Corbyn’s “wild conspiracy theories” but did not specifically rule out the presence of a customs border in the Irish Sea under their deal.

Mr Corbyn said: “We have now caught Johnson red-handed misrepresenting his own Brexit deal.”

The document, Mr Corbyn added, “drives a coach and horses through the prime minister’s claim that there will be, in his words, no border in the Irish Sea”.

Mr Corbyn highlighted page five of the document, which lists customs and security checks on exports from Northern Ireland to Great Britain as “potential fetters” to trade.

For goods travelling in the other direction, the document says tariffs, customs declarations on imports, checks on safety, security and regulations are possible issues.

The PM suggested last month that Brexit Secretary Stephen Barclay was wrong to say goods would face checks under his deal and Mr Johnson has been backed up by Julian Smith. Tory Party chair James Cleverly said: “The Conservatives have negotiated a great new deal with the EU which takes the whole of the UK, including Northern Ireland, out of the EU.”

Mr Corbyn was joined on the stage by shadow Brexit secretary Sir Keir Starmer, who said: “The issue of whether there are going to be checks is absolutely blown out of the water by this document, as is the suggestion that it won’t be bad for business.”

The Liberal Democrats welcomed the documents as evidence the PM “has been caught lying to the British public once again”.

TUV leader Jim Allister met secretary of state yesterday and said that in a “straight-talking meeting” he had “left Mr Smith in no doubt about the feeling of betrayal within Unionism and the united opposition across our community to the Boris deal which produces Brexit for Great Britain but not for Northern Ireland”.

• Yesterday the DUP expressed concern at the implications of Boris Johnson’s deal.

However, the party gave no hint that it will row back on its firm pledge not to back the man who most likely will be the only alternative prime minister, Jeremy Corbyn, in the event of a hung parliament.

Lagan Valley candidate Sir Jeffrey Donaldson, pictured, said the leaked document was “further demonstration that the prime minister’s deal would be bad for Northern Ireland”.

The DUP chief whip said: “The DUP warned the prime minister about this. Despite his protestations, the facts are in black and white. That is why we opposed the deal in the House of Commons and why Northern Ireland needs the deal changed.”

Sir Jeffrey added: “Jeremy Corbyn is using this as a campaigning tool but no unionist will be tricked by his rhetoric. He has in the past and would in the future work in cahoots with those who want to destroy the Union.”

UUP leader Steve Aiken said: “Arlene Foster and her colleagues bear a heavy responsibility for this crisis and they cannot continue in denial any longer. The public deserve to know which DUP MPs were involved in negotiations with the government in the run up to Johnson’s deal and what they agreed? They should also reveal what additional financial package they were offered in return for their support for a regulatory border in the Irish Sea.

“Northern Ireland faces a serious threat to its position within the United Kingdom. The DUP cannot hide or minimise the role they played in getting us here.”