Steve Baker, a former Brexit minister, accused Oliver Robbins, May’s chief civil service negotiator, and her most senior political aides of conspiring to bind Britain into a customs union with the EU in perpetuity.

Baker, who is now vice-chairman of the hardline European Research Group, led by Jacob Rees-Mogg, said May’s Europe advisers Denzil Davidson and Ed de Minckwitz should be dismissed because they ignored the advice of elected ministers.