Liz Truss faces a showdown meeting with a close ally of US president Joe Biden on Saturday amid international efforts to prevent the British government from overriding the Northern Ireland protocol.
The foreign secretary, and international trade secretary Anne-Marie Trevelyan, are due to hold talks in London with Congressman Richard Neal who is urging UK ministers against any unilateral “breach” of the Brexit treaty.
It follows a warning from house speaker Nancy Pelosi, who said the US Congress would not agree to any trade deal if Britain ploughs ahead with a plan to “discard” the protocol.
Mr Neal, who arrived in Brussels on Friday as part of a nine-member congressional delegation, also said Boris Johnson should uphold all parts of the Brexit withdrawal deal he signed in 2020.
“They haven’t breached it yet. They’re talking about breaching it, so part of my job is to convince them not to breach it,” the top Democrat told The Guardian.
“The broader occurrence here is that the protocol was duly negotiated by the British prime minister,” he told Politico. “It’s an international agreement that should be adhered to.”
“It’s not going to be the words of the UK – it’s going to be their actions,” he added. “I don’t think that Ireland, the Good Friday Agreement and the elections in the north [of Ireland] ought to be held hostage by a disagreement the UK has with the European Union.”
It comes as a senior official at the US State Department said the Biden administration did not want to see any “unilateral acts” with the protocol – warning that the row risked undermining western unity during the Ukraine war.
Secretary of state Antony Blinken’s adviser Derek Chollet told the BBC that a “big fight between the UK and the EU” was “the last thing” Washington wanted. “We want to see this issue resolved and we want to see the temperature lowered and no unilateral acts,” he said.
Mr Neal and fellow members of US congress are also set to meet Labour leader Sir Keir Starmer and shadow trade secretary Nick Thomas-Symonds on Saturday to discuss the Brexit row and the political impasse in Northern Ireland.
The American delegation is also expected to go to Belfast to meet Sinn Fein and DUP leaders, as well as visiting Dublin for talks with the Irish government, in the coming days.
Mr Johnson and Ms Truss have insisted they do not plan to tear up the protocol completely, but aim to unilaterally “fix” it through new legislation to override parts of the agreement with Brussels.
The foreign secretary said earlier this week the legislation would create a “green channel” for goods travelling from Great Britain to Northern Ireland. Only goods destined for the Republic of Ireland would be subject to customs checks.
Ms Pelosi said on Thursday that she had previously warned Mr Johnson and Ms Truss that if they chose to “undermine” the Good Friday Agreement, Congress “cannot and will not support a bilateral free trade agreement with the UK”.
DUP leader Sir Jeffrey Donaldson said Ms Pelosi’s intervention over the protocol row was “unhelpful” – but Sinn Fein’s vice president Michelle O’Neill “very much welcomed” the senior US figure’s remarks.
Both leaders met the Republic of Ireland’s premier, Micheal Martin, for talks in Belfast on Friday, as the impasse over power-sharing arrangements at Stormont rumbled on.
Mr Martin urged the DUP to help form Northern Ireland Executive as soon as possible, even if the unionist party wanted to engage in “parallel discussions” over the protocol.
The Irish premier said it was “unheard of” for a parliament not to convene after a democratic election, adding: “We can’t have a situation where one political party determines that the other political parties can’t convene in a parliament.”
Mr Martin also accused the UK government of moving “too far in a unilateral way” over the protocol. Calling for fresh UK-EU talks, he said it would mean “getting into the tunnel and negotiating in a serious way”.
He told the BBC: “I spoke to Boris Johnson and I have to nail this. This idea that somehow the European Union is being inflexible on this is just not the truth – it doesn’t stack up.”
But Sir Jeffrey said he had told the Irish premier that he is not interested in a “sticking plaster” approach to solving problems with border checks.
“It has to be fundamental change which respects Northern Ireland’s place within the UK internal market, and nothing short of that will suffice,” said the DUP boss.
The British ambassador to Ireland, Paul Johnston, played down concerns that the UK will never be satisfied with any changes to the protocol.
He said the government wants something that is “sustainable, has broader support and doesn’t make the protocol a wedge issue in Northern Ireland politics”, adding: “We want to get to a sustainable end date.”
