David Frost has said Liz Truss must not surrender to the EU by giving the European court of justice a role in trade disputes in Northern Ireland. On Tuesday, the former Brexit minister told the House of Lords European relations committee: “The court of justice cannot have a jurisdictional or arbitrational role in the future arrangement. I can’t see how they will be stable while that remained the case. I think better if that was acknowledged sooner rather than later.” Talks on the controversial issue of the Northern Ireland protocol were paused two months after Lord Frost quit his role in December but resumed last week amid rising hopes of an end to the dispute between the EU and the UK. One of Frost’s red lines in his eight-month negotiation with the EU over the protocol was the European court of justice (ECJ) and briefings to media suggest it may remain a divisive subject within the Conservative party. Earlier on Tuesday the thinktank UK in a Changing Europe said that the ECJ was not cited as a significant issue locally in Northern Ireland by voters or businesses. One of the authors of its new report on the Northern Ireland protocol bill said the row over the protocol had “escalated so grotesquely at a political level” it would be difficult to see how the unionists or the Eurosceptic European Research Group (ERG) of MPs could climb down and accept a compromise even on green v red lanes for trucks staying in Northern Ireland and those crossing the border to the republic. Frost told the House of Lords that the fragility in Northern Ireland politics made it difficult for the ECJ to be maintained. Peter Mandelson told the EU relations committee that if the politics of Brexit in Northern Ireland were fragile it was because Johnson signed the protocol “in bad faith”. Sitting beside Frost, Lord Mandelson, a former Northern Ireland secretary, told peers: “Nothing is ideally suited for the politics of Northern Ireland. That’s why you have to use creativity and flexibility in how you manage the sensitivity in the politics of Northern Ireland.” He was speaking as the second reading of the government’s Northern Ireland protocol bill was under way at the House of Lords. Conservative peer Patrick Cormack, a parliamentarian for the past 50 years, urged the government to pause the bill while negotiations were going on as did Labour peer Jenny Chapman. They decided not to put their amendments or motions of regret to a vote but to continue to find ways of delaying the bill when it returns to the committee stage in two weeks’ time.