If Sinn Fein win the poll, Mr Johnson would face attempting to secure changes to the protocol that are opposed by Northern Ireland’s first minister. 

Paul Givan, who was DUP first minister until his resignation last month, strongly supported the Government’s calls for changes to the protocol, amid concerns that the document’s requirements were harming Northern Ireland businesses.

Mrs Braverman and Mr Rees-Mogg are both former leaders of the European Research Group of Eurosceptic Tory MPs. David Jones, its deputy chairman, said that negotiations between Ms Truss and Maros Sefcovic, her EU counterpart, appeared to have become “bogged down” and said Article 16 should be triggered to revive serious negotiations.

“We need to find a way of getting it out of the mire and the best way of doing that is by invoking Article 16, which will be the precursor of a new negotiating mandate on behalf of the EU,” he said. “I think it ought to be done now.”

Lord Hayward said: “In Northern Ireland. I think there will be real constitutional issues, because for the first time Sinn Fein will actually come out as the largest single party in Northern Ireland.” He described Unionist parties as being “in a complete mess”, predicting that the Unionist vote would be split, allowing Sinn Fein to emerge as the largest party.

In an interview with The Telegraph, Ms Truss does not deny having shelved the idea of using the mechanism before May 5, simply insisting that Article 16 “remains on the table” as an option.