A carefully choreographed divorce deal between London and Brussels was derailed at the eleventh hour yesterday after Northern Ireland’s hardline Unionists rejected Theresa May’s agreement potentially to keep the province aligned with EU law after Brexit.

Mrs May, who travelled to Brussels to finalise the agreement with Jean-Claude Juncker, European Commission president, was forced to back away after the pro-Brexit Democratic Unionist party objected that it would prevent Northern Ireland from leaving the EU “on the same terms” as the rest of the UK.

The DUP provides the UK prime minister with her majority in parliament and it accused the Irish Republic, which had been engaged in weeks of talks with Mr Juncker and Mrs May to secure yesterday's divorce pact, of improperly meddling in Northern Ireland politics.