Julian Smith, leaving Downing Street yesterday, was forced to apologise to the Lib Dem MP Jo Swinson, who is on maternity leave and had been paired with Brandon Lewis

Julian Smith openly admitted to a rival chief whip that he intended to break a parliamentary convention in a crucial Brexit vote.

Mr Smith, the Tory chief whip, is facing calls to resign after The Times revealed that he urged three of his MPs to abandon pairing arrangements before the vote on Tuesday night, which the government won by just six votes.

Pairing allows MPs on different sides to agree not to vote so that an absence for illness, travel problems or maternity leave does not count against a member.

Jo Swinson is on maternity leave YUI MOK/PA

In a private meeting after the vote on the customs union, Mr Smith told his opposite number that he deliberately sought to break a pair involving Brandon Lewis, the Tory chairman, by summoning him to