Rishi Sunak is struggling to reconcile Tory MPs’ competing demands over his Rwanda plan, as would-be rebels warned that “major surgery” is still required to fix the flagship asylum legislation.

But it came as moderates from the opposite wing of the party said the Government must “stick to its guns”, warning that any further changes to appease the right-wingers would prove “unacceptable”.

In a day of drama in Westminster, various factions of the Conservative party met across the parliamentary estate as Mr Sunak and his ministers engaged in last-ditch efforts to win over potential rebels ahead of the Rwanda plans first Commons vote on Tuesday.

Amid turmoil over the plan,

– The One Nation grouping, which numbers around 100 MPs, agreed to recommended that its member back the Bill.

– Mr Sunak will meet with around 20 New Conservative MPs over breakfast, after the grouping convened a meeting in Westminster to discuss whether to abstain or vote down the plan.

– Downing Street insisted Mr Sunak would listen to the concerns voiced by the rival Conservative factions.

– Representatives from five groups on the Tory right considered the verdict of a “star chamber” of lawyers which decided the legislation needed significant changes.

The backing of the One Nation caucus was a boost to Mr Sunak, who spent most of Monday in front of the Covid-19 inquiry, and his hopes for getting the Bill through the key parliamentary stage.

But it came with a warning too, as chairman Damian Green said MPs would oppose any amendments that would risk the UK breaching the rule of law and its international obligations.

“We support the Bill unamended, but if anyone brings forward any amendments that breach our international obligations or breach the rule of law, we vote against those amendments at future stages.

“We will vote with the Government tomorrow, but we want the Government to stick to its guns and stick to the text of this Bill,” he told reporters as he left the meeting.

Across the parliamentary estate, the New Conservatives said that around 40 MPs – including former immigration minister Robert Jenrick and former home secretary Suella Braverman alongside senior MPs Sir Simon Clarke and Sir Jacob Rees-Mogg – gathered to discuss the Bill.

A spokesman warned: “Every member of that discussion said the Bill needs major surgery or replacement and they will be making that plain in the morning to the PM at breakfast and over the next 24 hours.”

The breakfast meeting comes as Mr Sunak faces perhaps the most serious test of his leadership so far. No government has suffered a defeat at a second reading since 1986.

Various ministers were deployed on Monday to brief MPs and win over wavering party colleagues, with Attorney General Victoria Prentis addressing the One Nation faction while Home Secretary James Cleverly spoke to MPs in a separate gathering in a Commons committee room.

Mr Cleverly said he was determined to get the legislation through after a meeting with Tory MPs in Parliament, calling it “important legislation”.

It came after Conservative backbench European Research Group chairman Mark Francois called on the Prime Minister to “pull” the legislation after lawyers convened by the caucus deemed it an “incomplete” solution to problems posed by small boat asylum claims.

The Bill, which Mr Sunak hopes will revive the stalled scheme to deport people crossing the English Channel to Kigali, would need “very significant amendments” to work, the so-called “star chamber” of legal advisers concluded.

We want the Government to stick to its guns and stick to the text of this Bill

Speaking after a summit of representatives from the “five families” – the ERG, the Conservative Growth Group, the Northern Research Group, the New Conservatives and the Common Sense Group – Mr Francois said: “It might be better to start again with a fresh Bill that is written on a different basis.”

In a rare move intended to win over critics, the Government produced a summary of its own legal position in support of the scheme on Monday.

The document concludes that there is a “clear lawful basis on which a responsible government may proceed” with a “novel and contentious” policy.

Mr Sunak has tried to find a middle ground in response to the Supreme Court ruling that his plan to send asylum seekers who arrive in the UK on small boats is unlawful.

His Bill allows ministers to disapply the Human Rights Act but does not go as far as overriding the European Convention on Human Rights.

The Government’s current assessment is that only one in 200 cases will successfully avoid being sent to Rwanda once the Bill becomes law.

But critics of the plan disputed the Home Office’s modelling of how effective it would be.

Mr Jenrick, in a post on social media, doubled down on his rebuke of the plan: “If individual claims are permitted everyone will make one, the court backlog will balloon, our detention capacity will become overwhelmed within days, people will be bailed, and new arrivals will simply abscond.

“The proposed bill is both legally and operationally fundamentally flawed.”

Mr Sunak won support from former Cabinet colleague Ben Wallace, who used an article in the Telegraph to warn his party not to “wreck” the Government over the issue.

The former defence secretary said that the vote should not become an “exercise of making the perfect (but unrealistic) the enemy of the good”.

No Government legislation since the Shops Bill in 1986 has fallen at second reading, but if all Labour and other opposition party MPs vote against it, a revolt by 29 Tories would be enough to defeat it.

Tories with concerns could instead choose to abstain or back the legislation at this stage but then seek to toughen it up – or water it down, depending on their views – as it progresses through the Commons.