‘There will be consequences’: No US trade deal if Boris Johnson reneges on Brexit agreement, Congressman warns

‘I can’t believe that any side would be acting in such a cavalier way when we're talking about a fragile peace in the North of Ireland’

The US will refuse to sign a trade deal if Boris Johnson reneges on protections for Northern Ireland in the Brexit agreement, a senior Congressman is warning.

The consequences for unpicking the deal – risking the return of a hard border in Ireland, Brendan Boyle said – would be the breakdown of talks with Washington, as well as Brussels.

The Democrat, who sits on a key Congressional committee, described the revelation that the prime minister plans to override the agreement he signed last year as “genuinely shocking”.

“If the UK does it in such a way that it violates the Good Friday Agreement, there will be no US-UK free trade agreement,” Mr Boyle said.

“So, the UK needs to understand there will be consequences that stretch well beyond trust dealings with the EU on this matter.”

He added: “I can’t believe that any side to this debate would be acting in such a cavalier way when we're talking about a fragile peace in the North of Ireland.”

Downing Street has denied that new legislation – to override requirements for customs checks in the Irish Sea and limits on using state aid – amount to tearing up parts of the Brexit agreement.

 They would only be used if talks with the EU failed, it says, but the move does amount to a unilateral act to rework an international agreement, alarming the EU.

It comes after Mr Johnson threatened to end the talks if there is no agreement by 15 October, while refusing to publish a state aid plan – which is vital to unlock them.

Ursula von der Leyen, the president of the European Commission, has described the agreement – praised by the prime minister last year – as “an obligation under international law”.

Mr Boyle, who sits on the ways and means committee, which has jurisdiction over all taxes and tariffs, said Nancy Pelosi, the House Speaker, had stated the same view.

“It will also be very difficult to enter into a trade negotiation with a party that would have just ripped up a very important agreement to us,” he told BBC Radio 4’s Today programme.

“Why would you engage in negotiations with such a party, because they might turn around and use the same tactic against you?”

The US trade talks have already stalled, dashing Mr Johnson’s hopes of a deal – long  hailed by Brexiteers as the big prize – before Donald Trump goes before the voters in November.

There is growing UK opposition to the US demand that the ban on acid-washed chicken and hormone-pumped beef must be lifted.

The trust problem was echoed by Gavin Barwell, Theresa May’s former chief of staff, who told Times Radio: “What would it do if we unilaterally change the terms of an international agreement we signed up to?

“First of all, it sends a very bad message to anyone else the UK might be negotiating with about our trustworthiness. But secondly, it's just going to make things much more difficult with the EU.”