The EU has comprehensively rejected British proposals for avoiding a hard border in Northern Ireland in a move which will cast serious doubt on the UK’s ability to leave the customs union, The Telegraph has learned.

Senior EU diplomatic sources said that Mrs May’s plan for avoiding a hard border in Northern Ireland was subjected to a “systematic and forensic annihilation” this week at a meeting between senior EU officials and Olly Robbins, the UK’s lead Brexit negotiator.

“It was a detailed and forensic rebuttal,” added the source who was directly briefed on the meeting in Brussels on Wednesday. “It was made clear that none of the UK’s customs options will work. None of them.”