Julian Smith, the chief whip, is facing calls to resign and criticism from fellow Conservatives after The Times revealed claims that he urged three Tory MPs to abandon “pairing” arrangements before a knife-edge vote on Tuesday.

Pairing is a parliamentary convention by which pairs of MPs on different sides of the Commons agree not to vote so that an absence for illness, travel problems or maternity leave, for example, does not count against a member.

Mr Smith summoned Brandon Lewis, the Tory chairman, from a meeting to parliament as a crunch vote on customs approached, witnesses claim.

The chief whip is understood to have told Mr Lewis that the later votes were going to be close and he needed him to vote. This breached a