A group of former cabinet ministers is planning a public intervention to try to show that the Conservative parliamentary party would support a "sensible" Brexit.
Justine Greening, Amber Rudd and Damian Green want to show the prime minister that she would have sufficient support to face down Brexit hardliners in her party.
Newsnight understands that their message has been supported in private by Julian Smith, the government chief whip.
In a pointed intervention, Mr Smith reportedly told members of the cabinet's Brexit cabinet sub-committee that they should, according to one witness, "get real" about the numbers in parliament.
The former cabinet ministers, who supported Remain in the EU referendum, have decided to act after concluding that it will not be possible to agree a Brexit deal that is accepted by all wings of the Conservative parliamentary party.
Talks with the Brexit-supporting European Research Group (ERG), led by Jacob Rees-Mogg, have persuaded members of the new group that there is little chance of finding common ground.
The group has won the support of some former Leave supporters, though none of these is so far willing to go public. One senior Leaver supporting the new initiative told Newsnight: "The prime minister will have to face down the ERG... maybe she also has to sack a cabinet minister."
In their discussions the group has decided that Theresa May has crucial numbers at Westminster at two levels:
- In the event of a vote of confidence in her leadership, the prime minister would have the support of at least half of the 316 Tory MPs. That would be enough to survive a confidence vote which the ERG could, theoretically, trigger with the support of just 48 MPs.
- Parliament as a whole would reject a no deal Brexit. It is calculated that up to 300 of the opposition and independent MPs would join at least 100 Tory MPs in voting down a no deal, passing the 322 MPs needed to secure a parliamentary majority.
No deal Brexit unlikely
A no deal end to the Brexit negotiations is seen as unlikely. But members of the new group believe that highlighting the prospect of such scenario - and how it would be rejected in parliament - can be used to persuade Theresa May that she would have a strong hand if she decided to challenge MPs advocating a no deal.
One senior figure in the new group told Newsnight: "The prime minister is going to have to make a decision. If she comes down on the side of the ERG to keep 60 of them happy that will be unacceptable to us and our numbers are larger.
"In the coming weeks we will be showing what the mainstream is thinking - Leavers and Remainers. This is about identifying a locus, where the mainstream lies to allow the prime minister to land this in the right place."
Antoinette Sandbach, the Conservative MP for Eddisbury who supported Remain, told Newsnight: "The decision was taken [in the referendum] that we would leave the political institutions of the EU but not how. That question of how we leave is incredibly important and why we need a pragmatic Brexit that preserves that close economic partnership whilst leaving the political institutions."
Ms Sandbach criticised Boris Johnson who recently described the so called "customs partnership", which has been supported by Theresa May, as "crazy".
The MP said: "My constituents don't like cabinet ministers openly rubbishing the plans of the prime minister in public. They want a sensible and considered compromise. Those that are arguing from an ideological perspective are in the wrong place compared to the vast majority of us at Westminster."
'No deal better than a bad deal'
Daniel Hannan, the Conservative MEP who was a prominent Leave campaigner, said that the vast majority of Conservative MPs want a Brexit to restore sovereign control to the UK but which also provides for the "closest relationship with our European neighbours".
But Mr Hannan warned that the UK may be forced to accept a no deal. "No deal is plainly better than a bad deal... Imagine that you were buying a car and you said to the car dealer: 'I am definitely going to walk out of this showroom with your vehicle, now let's sit down and haggle about the price.' That would be a ridiculous position."
A source in the ERG dismissed the proposed intervention. The source pointed out that seven Brexit-leaning Conservative MPs, who are not in the ERG, would withdraw their support from Theresa May if she negotiated a deal they found unacceptable. This would cancel out her parliamentary majority which she assembled last year with support from the DUP.