Tory backbenchers are plotting a “guerrilla” campaign to derail Theresa May’s Brexit plan – even if she wins the crunch Commons vote on her deal next month.

Both Brexiteer and Remainer MPs have spotted that they can launch a last-ditch bid to change the proposals by amending the detailed legislation needed to implement any divorce agreement with the EU, HuffPost UK has learned.

A raft of “killer” amendments to the Withdrawal and Implementation Bill are planned by both sides, with the aim of forcing the Prime Minister back to the negotiating table in Brussels.

With Labour support, the rebels hope that they can fight a rearguard action in the New Year to get their way, even if May somehow squeaks a narrow victory in the meaningful vote in the Commons in December.

Crucially, if the Withdrawal Bill in any way materially alters the deal struck by May with the EU, it could ruin parallel attempts to ratify the Withdrawal Agreement in the European Parliament.

The fresh threat to May’s authority came amid renewed claims from some Brexiteers that an ‘imminent’ move against the PM was likely, with more MPs sending in letters to party chiefs to demand a vote of no confidence in her.

One key figure within the 80-strong backbench European Research Group (ERG), which is chaired by Jacob Rees-Mogg, said that the “guerrilla warfare” would allow MPs to wear down the whips and No.10.

“People would need to stock up on book about Algeria or Vietnam, as the wars there would set the template,” the source said.

“Them winning hardly means us losing. We don’t need to get lucky much more than once. It’s always, and ever more pressingly so, in Corbyn’s tactical interest to support us.”

Another Brexiteer added: “If May were to force through the meaningful vote with Labour support, the ERG would then wreck the legislation and so the deal would not be ratified by the UK.”

While the “meaningful” vote motion due in December has hugely symbolic power and can be interpreted as intention of ratification of the agreement, the actual legislation is seen as more important by some legal experts.

One Labour source said that the party was also aware of the potential for the Withdrawal and Implementation Bill to give it another chance to push for its own version of Brexit.

A key amendment for Labour could be to commit the PM to renegotiating a permanent customs union, a move that could attract Tory Remainer MPs. 

Some MPs may also seek to make the bill conditional on a “People’s Vote”, a new referendum on the deal. Eurosceptics, for their part, could seek to turn the legislation into proposals for a ‘no-deal’ or World Trade Organisation rules.

Anand Menon, director of the UK in a Changing EU think tank, said that the historic precedents had been set during the passage of the legislation that first made the UK a member of the European Economic Community in the 1970s.

“The sceptics get two bites at the cherry. The equivalent in 1972 was there was a majority about 80 for the [main] agreement with the European community to join. But there was a majority of just 8 for European Communities Act,” Menon said.

“When MPs see the detail in the legislation they may change their mind. You have to go through the whole Parliamentary process twice, except the second time round MPs will have had Christmas probably to sit down and ponder what they really think and to consult amongst themselves.

“They get a longer Parliamentary process in which to cause trouble. The interesting thing is when that bill is going through Parliament the European Parliament will already have started its consideration in parallel based on the fact that we had agreed it in Parliament once and things could get very, very messy at that point.

“If the amendments substantively alter the withdrawal agreement, then we have rejected it.”

The 2018 EU Withdrawal Act passed this year stated that the Government would not be able to ratify the withdrawal agreement unless four conditions were met.

The conditions were: publication of the documents, a Commons resolution motion was passed, a debate had taken place in the House of Lords and Parliament had passed legislation needed for implementation.

A spokeswoman for the Department for Exiting the European Union said: “We fully expect that Parliament, having approved the deal, would pass the legislation which implements that deal.”

Meanwhile, fears of a leadership threat to May were heightened on Wednesday night. It appeared some members of the ERG had shifted their position and were ready to write letters to the chairman of the backbench 1922 Committee calling for a confidence vote.

A total of 48 such letters, 15% of the Parliamentary party, are required to trigger such a vote.

Backbencher Conor Burns, a former aide to Boris Johnson, told Sky News: “There comes a point where if the PM is insistent that she will not change the policy, then the only way to change the policy is to change the personnel”