A fresh Conservative revolt this week could force Theresa May to abandon her hopes to keep her plans for Brexit secret.

Up to 40 Tory backbenchers are believed to be ready to vote with Labour to bind the Prime Minister into “publishing the government’s plan for leaving the EU before Article 50 is invoked”.

The motion, to be debated on Wednesday, demands the government set out its broad aims for Brexit – its stance on the single market, on freedom of movement of EU citizens, and on security matters, for example.

Until now, Ms May has refused to make such a commitment, arguing that “showing the government’s hand” will weaken its position in the negotiations to follow.

But – faced with the revolt – she may be forced to give way or face the humiliation of being defeated by the Labour motion.

Anna Soubry, a key pro-Remain Tory MP, said: “I have to say I can't see anything in it I don't approve of and could not support.”

She urged the Prime Minister to put down her own “sensible amendment” – telling BBC Radio 4's World At One: "These things are incredibly important. This actually transcends party politics and tribalism.”

Ms Soubry suggested scores of Conservative backbenches were concerned that the government’s Brexit strategy was not being put under the microscope.

Veteran former Cabinet minister Ken Clarke told The Independent he would join Ms Soubry, saying: "I plan to support the Labour motion on Article 50 in what appears to be its current form."

The clash threatens a rerun of a Labour motion two months ago, which merely demanded “proper” Parliamentary scrutiny of the exit plan by the Commons.

On that occasion, to avoid a damaging backbench rebellion, the Prime Minister was forced to effectively give it her backing.

The debate also gave a platform to a string of former Conservative ministers to warn that the lack of a coherent plan for leaving the EU was hurting the economy.

If there is a similar climbdown before Wednesday afternoon, it could commit the government to publish a white or green paper ahead of the triggering of the Article 50 notice.

Ms May still intends to do that before the end of March – although that timetable could be derailed by the Supreme Court case into whether Parliament must first give its consent.

The motion, tabled by Jeremy Corbyn and Keir Starmer, his Brexit spokesman, appears carefully crafted to attract as much Conservative support as possible.

It acknowledges there “should be no disclosure of material that could be reasonably judged to damage the UK in any negotiations to depart from the European Union”.

Some pro-Brexit Tory MPs are also expected to back it – as they fear some ministers are backsliding on a clean withdrawal and want to see the government’s strategy.

There was fresh confusion at the weekend when Boris Johnson dismissed the idea of significant payments to retain access to the single market – just days after Brexit Secretary David Davis suggested they would be necessary.

Labour has pointed out that command papers and economic impact papers were put before MPs before Britain entered the then-EEC in 1973 – arguing for the same.

Jenny Chapman, a junior Brexit spokeswoman, protested that MPs had to make do with “side comments” from ministers, or “leaked documents”.