THERESA May continues to stand by her beleaguered chief whip in the crunch Brexit vote cheating row.

Yesterday, the Prime Minister insisted that Julian Smith had made an “honest mistake” when he ordered Tory Party chairman Brandon Lewis to break a pairing agreement with Liberal Democrat MP Jo Swinson, who is currently on maternity leave.

That followed revelations on Thursday night that Smith had said he was deliberately going to break the pair because the vote on the customs union was tight.

Pairing is where MPs from different parties effectively cancel each other out in the votes.

If one MP cannot physically be in the Commons, because of illness, travel problems, or maternity leave, then they can “pair” with a rival MP, who will be excused from walking through the lobbies.

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

However, Lewis took part in a key vote, which the Government won with a majority of just six.

According to newspaper allegations, Smith also urged three other Tory MPs to abandon “pairing” arrangements, though it seems none of them did.

Asked about the issue following her speech in Belfast on Friday, May said: “There was an honest mistake made, for which the chief whip and indeed Brandon Lewis have both apologised to the member concerned.”

The East Dunbartonshire politician wasn’t for accepting the Prime Minister’s excuse.

“Do you mean, Theresa May, ‘We honestly intended to screw over someone else’?” she tweeted.

“Because evidence is mounting that pairing was deliberately broken – not a mistake as claimed.”

The SNP’s leader at Westminster, Ian Blackford, said Smith needed to go.

“It was not a mistake that Brandon Lewis broke his pairing arrangement, it was under the instruction of Julian Smith.

“This is inexcusable, a clear and blatant breach of trust with Jo Swinson and undermines parliamentary democracy. If Julian had any sense of decency he would resign”.

He added: “His next statement should be his resignation for the appalling behaviour which demeans Parliament. Breaking the pairing agreement was no mistake, it was a breach of trust.”

Labour also called on May to sack the two men. Deputy leader Tom Watson said: “It is unbelievable that the Prime Minister has repeated the desperate and blatantly untrue excuses made by her party chair and chief whip.

“This is a serious issue that goes beyond efficient administration in the House of Commons. This is about public trust in politics. At such a crucial time for our country, people expect candour and decency, not cowardice and dishonesty.

“Theresa May was right to call the Tories the ‘nasty party’, and nothing has changed.

“From forcing seriously ill MPs into the Commons in their wheelchairs, carrying sick buckets, to cheating a new mum out of her vote, this Government is rotten to its core.

“If Brandon Lewis and Julian Smith, two generals of the nasty party, don’t have the honour to resign, the Prime Minister should find the strength to sack them.”

Former Tory deputy Prime Minister Michael Heseltine, said there was no excuse for “breaking one’s word”.

He told the BBC: “It is to me unthinkable that the biggest peacetime political disaster of my life is being forced through the House of Commons with any device, threat, chicanery that the Government can turn its hands to.”