No 10 believed to be trying to get MPs to approve only the withdrawal agreement

Theresa May is still aiming to hold a vote on her Brexit deal on Friday, even though there are no new talks with the Democratic Unionist party (DUP) and more Tory Eurosceptics have hardened their positions against it.

No 10 is believed to be attempting to get MPs to approve just the withdrawal agreement governing how the UK will leave the EU, while setting aside the political declaration that governs the future relationship.

The hope is that some MPs from other parties could switch sides if they are not voting on the political declaration, which has been rejected by Labour because it does not say the UK will remain in a customs union.

What could happen if May’s Brexit deal is voted down again? Read more

May’s de facto deputy, David Lidington, appeared to hint at this by urging MPs to back the withdrawal agreement irrespective of their opinions about the latter.

“If you believe in delivering the referendum result by leaving the EU with a deal then it is necessary to back the withdrawal agreement,” he told the British Chambers of Commerce conference in London.

“Whether a particular MP wants the final destination to look like Norway or look like Canada or look like the proposals in the Chequers white paper, the starting point is the withdrawal agreement itself.”

Some Labour MPs have been approached by Conservative whips about the plan to split the withdrawal agreement and political declaration. However, Labour said it could not vote for leaving the EU without an idea of where the UK was heading in its relationship.

The government is also contemplating the move in order to secure a longer extension to article 50, as the EU only requires the passing of the withdrawal agreement to move the exit date from April 12 to May 22.

Keir Starmer, the shadow Brexit secretary, warned MPs that the Tory leadership contest meant it could be a “Boris Johnson Brexit, a Jacob Rees-Mogg Brexit, or a Michael Gove Brexit”.

He added: “If the prime minister tries to separate the withdrawal agreement and the political declaration altogether, that only makes matters worse.

“We would be leaving the EU, but with absolutely no idea where we are heading. That cannot be acceptable and Labour will not vote for it.”

No 10 also acknowledges that the withdrawal agreement and political declaration would both ultimately have to be passed through parliament in order to leave the EU.

Play Video 1:11 Deal or no deal: Jacob Rees-Mogg flip-flops on Theresa May's Brexit agreement – video

The chances of the deal making it through the House of Commons remain slim, with at least 20 and probably more like 30 Eurosceptics still holding out.

Boris Johnson, the Tory leadership hopeful who had said he would reluctantly support the deal, said it was “dead anyway”, and others joined the list of those who will not vote for it, including Adam Afriyie, Bernard Jenkin, Bill Cash and Dominic Raab.

Raab, another leadership contender, positioned himself as the “no-deal” candidate on Thursday by urging May to “go back to the EU again” to press for changes to the deal, which Brussels has already ruled out.

The DUP, which has 10 MPs and provides May with her majority through a confidence and supply deal, said on Wednesday night it could not support the withdrawal agreement because it threatens the union. A party source said on Thursday there were “no talks today”, fuelling speculation they had been shelved entirely.

But despite the ominous signs for May’s deal, Andrea Leadsom, the leader of the Commons, told MPs they would sit on Friday to debate a government motion on Brexit again.

Leadsom said only that the vote would get around the ruling of the Speaker, John Bercow, that the same motion could not be voted for a third time.

“The motion tabled will comply with the Speaker’s ruling but the only way we ensure we leave in good time on 22 May is by approving the withdrawal agreement by 11pm on 29 March, which is tomorrow,” she said, adding: “It’s crucial we make every effort to give effect to that and to allow the house to debate this important issue.”

Leadsom was also asked whether ministers wanted to decouple the withdrawal agreement for a separate vote, but declined to specify, saying MPs would have to await the motion.

The Labour MP Ben Bradshaw, who fears the motion could be “more trickery”, said it would not be illegal for the government to seek to pass just the withdrawal agreement, without MPs having a say on the plan for the future relationship.

Brexit is a national crisis. Not a careers fair for 22 Tories | Aditya Chakrabortty Read more

A spokeswoman for the Commons leader’s office said: “Discussions are ongoing and we will look to table the motion as soon as possible [on Thursday], in order to avoid asking for another extension and the requirement to undertake European parliament elections.”

Downing Street sources insisted talks were continuing with the DUP in the hope of a breakthrough.

The DUP’s main objection is to the backstop, the “insurance policy” designed to avoid the return of border checkpoints in the event a future trade deal is not agreed.

It argues that the measure would result in Northern Ireland having to abide by different trade rules to the rest of the UK, which Arlene Foster, the DUP leader, says would “damage the union”.

Hopes that this might mean that the DUP could abstain on a future vote were dashed on Wednesday night after Nigel Dodds, the party’s deputy leader, said: “The DUP do not abstain on the union.”

A spokesman for the DUP said the backstop had “the potential to create an internal trade border within the United Kingdom and would cut us off from our main internal market, being Great Britain”.

He added: “The backstop, which we warned this government against from its first inception, poses an unacceptable threat to the integrity of the United Kingdom and will inevitably limit the United Kingdom’s ability to negotiate on the type of future relationship with the EU.”