THE UK FOREIGN Secretary is set to meet with a top US Democrat today as tensions mount over the UK’s controversial plans to overwrite parts of the Northern Ireland Protocol.

Liz Truss and International Trade Secretary Anne-Marie Trevelyan are expected to hold meetings with a bipartisan congressional delegation led by Richard Neal, who heads up the powerful ways and means committee in the US House of Representatives.

Taoiseach Micheál Martin said yesterday there was “no substitute” for substantive negotiations between the UK Government and EU to resolve difficulties with protocol.

During a visit to the north where he met with party leaders, he also said an Assembly and Executive should be formed at Stormont while those negotiations continued, and accused the UK of “moving the goalposts” over its approach to the protocol.

Today’s meeting follows a warning from US House speaker Nancy Pelosi that Congress will not support a free trade agreement with the UK if Boris Johnson’s government persists with “deeply concerning” plans to “unilaterally discard” the protocol.

In a strongly-worded intervention, Pelosi urged the UK and the EU to continue negotiations on the post-Brexit trade arrangements to uphold peace in the region.

The congresswoman said in a statement: “The Good Friday Accords are the bedrock of peace in Northern Ireland and a beacon of hope for the entire world.

“Ensuring there remains no physical border between the Irish Republic and Northern Ireland is absolutely necessary for upholding this landmark agreement, which has transformed Northern Ireland.

“It is deeply concerning that the United Kingdom now seeks to unilaterally discard the Northern Ireland Protocol, which preserves the important progress and stability forged by the Accords.”

The latest controversy has been sparked by Truss’s announcement on Tuesday that the UK intends to legislate to override parts of the Brexit withdrawal treaty it struck with the EU.

The Foreign Secretary told the Commons the move was needed to reduce “unnecessary bureaucracy” and to protect the Good Friday Agreement, arguing that the EU’s proposals “would go backward from the situation we have today”.

The ongoing row over the treaty has created an impasse in efforts to form a devolved government administration in Belfast, with the Democratic Unionist Party (DUP) refusing to join an executive unless its concerns over the situation are addressed.

Pelosi’s intervention was met with scorn from former Brexit minister Lord Frost, who called the statement “ignorant” of the “the realities in Northern Ireland”.

“There is no plan to put in place a physical border,” he told the BBC.

“Nobody has ever suggested that, so I don’t know why she is suggesting that in her statement.”

DUP leader Jeffrey Donaldson also described Pelosi’s contribution as “entirely unhelpful”.

Pelosi is not the only senior figure in Washington to express concern about relations between the UK and the EU in recent days.

Derek Chollet, a senior adviser to the US Secretary of State, Antony Blinken, said yesterday that a “big fight” between the UK and the EU was the “last thing” the US wanted.

Neal told The Guardian part of his job is to convince the UK not to breach the Brexit treaty.

“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,” he said

“My purpose is manifold but we really want to reaffirm America’s unwavering commitment to the Good Friday Agreement and to remind everybody that on the eve of the 25th anniversary of the Good Friday Agreement, it has worked splendidly.

“I want to remind everybody in the UK, in Northern Ireland that it should not be treated as a cavalier achievement.”

He is also expected to meet with the Labour leader Keir Starmer and shadow international trade secretary Nick Thomas-Symonds.