In BBC leader debate Jeremy Corbyn and Boris Johnson clash over Irish Sea border barriers and Labour leader’s past stance on IRA

On Friday night’s head to head contest between the pair, Mr Corbyn reiterated claims that the Labour Party made earlier in the day about leaked Treasury documents, while Mr Johnson said he found it “curious” to be lectured by someone who supported the IRA violent campaign to destroy the Union.

Mr Corbyn said the leaked documents show “clearly” that there will be charges and customs checks on Northern Ireland-Great Britain trade.

He said: “... And as the documents we have shown today indicate he hasn’t been exactly straightforward on the issues surrounding trade with Northern Ireland and the Republic of Ireland. So I do think we need a bit of openness from the government.”

Mr Corbyn added that the documents “show quite clearly that there are going to be charges, there are going to be customs checks, there are going to be restrictions on trade between Britain and Northern Ireland”.

The prime minister replied: “Ah well actually that is not true, the whole of the UK comes out, England, Scotland, Wales, Northern Ireland, together, we do free trade deals together, Northern Ireland is part of the customs territory of the UK, and we are united, and I have to say, I think it’s a great opportunity for our country.”

Mr Corbyn then held up a paper that said HM Treasury document entitled NI Protocol.

Mr Johnson said: “It says unfettered access I think is what it says.”

Mr Corbyn said: “It says unfettered access and also it questions the fettering that will happen.”

The prime minister said that “the document also says is that Northern Ireland is part of the customs territory of the UK”.

The debate host Nick Robinson then asked: “But isn’t the problem Mr Johnson that the DUP, the unionists who were your partners, they agree with him and not with you?”

Mr Johnson replied: “No they don’t actually because our deal is a great deal. But let me just make one point, I do find it slightly curious to say the least Nick, to be lectured about the Union between Great Britain and Northern Ireland by a man who all his life, political life, has campaigned to break up that union and actually supported, for four decades, the IRA in their campaign violently, violently, to destroy it, I must say I find it a curiosity.”

Mr Corbyn said: “How about the prime minister showing a degree of honesty about the arrangements he has actually made with Northern Ireland> He spoke at a DUP conference and said there would be no restrictions whatsoever. We now know there are restrictions. He should and could have said that at the time.

“And so it is a question of openness on all of this.”

Mr Robinson then asked the Labour leader about his alleged lack of belief in the United Kingdom.

He replied: “What I have done is always wanted to see a peace process in Northern Ireland and that is exactly what we have got and thank you to the Labour government that negotiated it after 1997.”