Moderates from the One Nation group will back Rishi Sunak’s Rwanda plan, in a boost to the Prime Minister amid last-ditch efforts to win over would-be rebels.

The One Nation grouping of Tory MPs has said that it has recommended its members back the plan, but warned that it would oppose any amendments that would risk the UK breaching the rule of law and its international obligations.

Damian Green, who chairs the influential caucus of more centrist MPs, said: “We have taken the decision that the most important thing at this stage is to support the Bill despite our real concerns.

“We strongly urge the Government to stand firm against any attempt to amend the Bill in a way that would make it unacceptable to those who believe that support for the rule of law is a basic Conservative principle.”

The Prime Minister has faced calls from the Tory right to scrap the Safety of Rwanda Bill before it faces its first Commons vote on Tuesday because it is not “fit for purpose”.

But Home Secretary James Cleverly said he was determined to get the legislation through after a meeting with Tory MPs in Parliament.

A meeting convened by the New Conservatives also met on the parliamentary estate on Monday evening, with over 20 MPs in attendance at the office of backbencher Danny Kruger.

Former immigration minister Robert Jenrick and former home secretary Suella Braverman were among those attending, alongside senior MPs Sir Simon Clarke and Sir Jacob Rees-Mogg.

The same grouping, mainly drawn from MPs elected in 2019, will attend a breakfast meeting hosted by Mr Sunak at Number 10 ahead of Cabinet he seeks to tackle the competing concerns of his restive backbenchers.

A spokesman for the group did not say how New Conservatives would vote, but warned the Bill “needs major surgery or replacement”.

“They will be making that plain in the morning to the PM at breakfast and over the next 24 hours,” he said.

Mr Sunak’s authority faces a test when the Bill has its second reading vote on Tuesday – no government has suffered a defeat at this stage of a proposed law’s progress since 1986.

The support of the One Nation grouping could prove crucial in ensuring the legislation moves onto the next parliamentary stage, but Mr Green also had a warning for Mr Sunak ahead of the vote.

“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 on Monday night. This could prove a headache for the Prime Minister, if he faces pressure from right-wingers to toughen up the flagship legislation.

The gathering of centrist MPs was addressed by Attorney General Victoria Prentis, the latest Cabinet minister sent out to brief MPs on the contents of the Rwanda plan.

Mr Cleverly said he was determined to get the legislation through after a separate meeting with Tory MPs in a parliamentary committee room.

On a day of drama in Westminster:

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

– Various factions of the party met on the parliamentary estate to discuss the legislation, with the New Conservatives still silent their plan for Tuesday.

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

The Home Secretary, who spoke to MPs in a Commons committee room on Monday afternoon, said the Bill was “important legislation” and “we are determined to get it through”.

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.”

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.