Rishi Sunak and James Cleverly are engaged in last-ditch efforts to persuade would-be Tory rebels to back the Government’s Rwanda plan.

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 Mr Cleverly said he was determined to get the legislation through after a meeting with Tory MPs in Parliament.

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.

– Moderates from the One Nation group were expected to hold a separate meeting to air their concerns that the legislation may already go too far.

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

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 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.

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.”

Asked whether the proposal risked delaying the £290 million scheme even further, he told the PA news agency: “That is infinitely preferable to powering on with a piece of legislation which at the end of the day is not fit for purpose.”

He refused to say whether he still had confidence in the Prime Minister, whose leadership is on the line if the Bill fails to gain enough support from Tory MPs.

Mr Sunak’s ability to address Tory concerns at Westminster on Monday was limited as he appeared at the Covid inquiry, but he will host a breakfast meeting with members of the New Conservative group ahead of Cabinet on Tuesday.

Mr Cleverly spoke to MPs in a Commons committee room on Monday afternoon and said the Bill was “important legislation” and “we are determined to get it through”.

But in its assessment, the star chamber said: “The Prime Minister may well be right when he claims that this is the ‘toughest piece of migration legislation ever put forward by a UK Government’, but we do not believe that it goes far enough to deliver the policy as intended.”

The lawyers warned that the legislation would not prevent asylum seekers making individual claims against being sent to Rwanda and they argued it did not go far enough to address the risk of the European Court of Human Rights blocking the plan.

The ERG was holding a further meeting on Monday evening along with members of the Common Sense Group and New Conservatives, which is expected to be addressed by former immigration minister Robert Jenrick, who resigned in protest at the legislation.

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.

A senior Tory source said: “There was never any modelling done for the new Rwanda Bill because they failed to plan. Even this old, optimistic model says it could take more than two months to remove a migrant. It would be laughable if it wasn’t so serious.”

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.