Theresa May’s efforts to secure a Brexit deal by the end of March have suffered a serious setback after it emerged that UK and European Union negotiators were struggling to bridge the gap over the Irish border backstop in time for a November summit.

The prime minister was forced to admit that “significant” issues remained despite talks that went on until the early hours of Monday morning. Unless there is dramatic progress by the end of Wednesday, the exit timetable will become increasingly squeezed.