Brussels and Dublin will raise doubts about Britain’s commitment to the Brexit deal in Washington on Wednesday in a bid to heap pressure on the UK to back down in the row over the Northern Ireland Protocol.

Maros Sefcovic, the European Commission vice-president, and Simon Coveney, the Irish foreign affairs minister, will brief the Friends of Ireland caucus of US Congressmen on Capitol Hill.

Brussels was infuriated by the UK’s unilateral decision to extend grace periods on food checks on goods exported from GB to Northern Ireland, which it says violates the terms of the Brexit treaty.

The meeting will be seen as a bid to maximise leverage over the UK, which hankers after a trade deal with the US to cement its post Brexit Global Britain agenda.

Joe Biden, the US president, said in September last year that any UK-US trade deal hinged on continued respect for the Good Friday Agreement.

Mr Biden, who is proud of his Irish roots, made the comments after the UK threatened to override the Withdrawal Agreement, which prevents a hard border on the island of Ireland.

The briefing will take place a week before the annual St Patrick’s Day celebration.

Micheál Martin, the taoiseach, is expected to raise the latest Brexit developments during a call with Mr Biden, who is said to be unequivocal in his support for the Good Friday Agreement, next Wednesday.

Mr Sefcovic briefed EU ambassadors on the possible response to the UK unilateral action on Tuesday night in Brussels.

The commission is expected to launch legal action in the European Court of Justice, which retains jurisdiction over the Northern Ireland Protocol, “very soon”. It could also trigger enforcement measures in the Withdrawal Agreement, although no final decision was taken on Tuesday night.

EU ambassadors were said to have been angered by Lord Frost’s accusation the EU was still “sulking” over Brexit. They discussed continuing to deny access to the Single Market for the City of London to maximise leverage over Britain.