The visiting US congressional delegation had a forceful and at times heated encounter with pro-Brexit UK hardliners as the American politicians rejected claims that the Border was a “concocted” issue.

The delegation, led by the Speaker of the US House of Representatives Nancy Pelosi, met members of the pro-Brexit European Research Group, led by Conservative MP Jacob Rees-Mogg, on Monday. The meeting was part of their mission to the UK and Ireland this week to stress that there was no chance of a US-UK trade deal if Brexit damaged the Northern Irish peace process.

Democratic congressman Brendan Boyle, one of the members of the travelling delegation, said the US politicians had a “frank discussion” with the ERG that was “a good, sincere, honest exchange”.

The Pennsylvania representative said the delegation’s warning about any post-Brexit risk to the peace process jeopardising any future UK-US trade deal and the challenge of passing any trade deal through the US congress amid the current climate “acted as a reality check” on some UK politicians they met.

“A number of the ERG members were not exactly pleased with what they heard from the US side,” he said.

The two-term congressman said the overwhelming majority of the UK politicians they met appreciated the position of the US delegation and “the constructive role that we are playing”.

“The one exception clearly was the ERG who never explicitly accused us of taking sides but, as they expressed it, it is clear that their world view is that the Border issue is ‘concocted’ and that it is really just being used by Remainers in London, Brussels, Dublin and Washington all in some sort of grand conspiracy to force them to do something that they don’t want to do,” said Mr Boyle.

Mr Rees-Mogg told the delegation during their meeting that the ERG included two former Northern Ireland secretaries of state, Theresa Villiers and Owen Paterson.

Mr Boyle said the delegation attempted to argue against the ERG’s characterisation of the US role.

“We very much attempted to disabuse them of that sort of conspiracy-type thinking,” he said.

The Philadelphia politician, the only House member with an Irish-born parent, noted the positive role played by the US in the peace process and how this was ultimately applauded by the UK.

“The idea that some folks in London, Dublin, Brussels and Washington DC are all acting together as part of some grand conspiracy in making up our concerns for a re-establishment of a hard border is a world view that is extremely difficult for me to understand,” said Mr Boyle.

The Democrat said the appointment of a US special envoy by the Trump administration could prove “constructive and helpful” in the Brexit process, particularly in the absence of a Northern Ireland Assembly.