THERESA May has been accused of telling an “untruth” in Parliament over the furore of the MP “cheated” out of a vote during Tuesday’s crunch Brexit vote.

The claim follows reports that Tory chief whip Julian Smith reportedly told a rival party’s whip that he was deliberately going to break pairing arrangements.

Pairing, where MPs from different parties effectively cancel each other out in missing votes, is a long-held parliamentary convention.

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If one MP cannot physically be in the Commons, because of illness, travel problems, or maternity leave, then the party whips arrange a “pair” with a rival MP, who will be told not to walk through the lobbies.

On Tuesday night, when the government teetered on the brink over a vote on the Brexit trade bill, Tory MP Brandon Lewis was supposed to have been paired with East Dunbartonshire LibDem Jo Swinson, who gave birth to her son Gabriel just two weeks ago.

However, Lewis took part in a division on the customs union that the Government won by just six votes.

Swinson was sceptical that it was a mistake. She tweeted: “There’s a word for it – cheating.”

According to newspaper reports, Smith also urged three other Tory MPs to abandon “pairing” arrangements, although it appears none did.

The other parties’ whips are furious with the Tory. While the whole convention of pairing may seem particularly procedural, with the Government having a notional majority of just 10, it would take very little for May to be defeated.

One report said Smith told his opposite number in a rival party that he deliberately sought to break a pair involving Brandon Lewis, the Tory chairman. However, Smith then apparently apologised to the rival chief whip because he did not realise that Lewis was paired with an MP on maternity leave. He claimed that if he had realised, he would have chosen a different pair to break.

Questions will now be asked of the Prime Minister, who on Wednesday told the Commons, the “breaking of the pair was done in error”.

Shadow equalities secretary Dawn Butler said: “If these reports are correct, the Tory whips, Brandon Lewis and even the Prime Minister have been telling untruths about their shocking move against an MP on maternity leave.”

LibDem MP Christine Jardine said Smith should be sacked: “These allegations completely undermine the trust on which the pairing system depends. Cynical abuse to get the government through a difficult day is a sure fire way to corrode that trust. This situation is so serious that Downing Street can keep the system or they can save their chief whip.”