Theresa May will be guilty of telling MPs a “straight-up lie” if she cancels crunch votes this week that would allow them to force a delay to Brexit, Yvette Cooper says.

The former Labour leadership contender also said the prime minister would be “frit” if, as rumoured, she abstained on whether to rule out a no-deal Brexit – or even left the country to avoid the vote.

The comments came amid rumours that Ms May is poised to pull the second “meaningful vote” on her stalled deal, faced with the prospect of another crushing defeat, and later votes on vetoing a crash-out Brexit.

Ms Cooper vowed to work with backbench Conservatives to ensure the Commons can seize control of the Brexit agenda, if the prime minister goes back on any of the promises made last month.

Those pledges – made at the despatch box – were a vote on the deal on Tuesday, on ruling out a no-deal on Wednesday if the agreement is rejected and, if it is vetoed, a Thursday showdown on extending Article 50.

Speaking at a think-tank event, Ms Cooper said: “There are rumours that the prime minister will pull the vote tomorrow and then pull the vote on Wednesday and Thursday too

“Whatever she does tomorrow, I don’t think she will pull the votes on no-deal and extending Article 50.

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“She gave me her word, she gave parliament her word – I don’t believe the prime minister would straight-up lie on something so important as this.”

The warning was echoed by former Tory minister Nick Boles, who has worked with Ms Cooper to force the government to seek a Brexit delay if her deal cannot pass.

“I am sure that the prime minister will honour these three commitments. If she doesn’t she will forfeit the confidence of the House of Commons,” Mr Boles tweeted.

Downing Street insisted the meaningful vote would go ahead on Tuesday – but would not be specific about what exactly MPs will be voting on.

The prime minister’s spokesman refused to deny she could hold a provisional vote on the hypothetical deal she is seeking in Brussels – with tweaks to the Irish backstop – rather than on the deal as agreed.

Furthermore, MPs may not know until much later today, as he government has until around 10pm to table the motion for debate.

Speaking to the Centre for European Reform, Ms Cooper also expressed incredulity that Ms May could abstain on a no-deal, or even ensure she was absent from the vote.

“I can’t believe that will be true either. She is the prime minister – she cannot be frit.”