Rishi Sunak’s emergency Rwanda legislation has been given only a “50% at best” chance of successfully getting removal flights off next year in an official legal assessment for the Government.

Attorney General Victoria Prentis has been told that the legislation leaves a significant risk of the European Court of Human Rights blocking planes to Kigali, the Times first reported.

The assessment is likely to toughen the Prime Minister’s battle to get his divided Tory MPs to support his new Bill that he hopes will revive the stalled £290 million policy.

Meanwhile, Robert Jenrick, who resigned as immigration minister over the legislation, has argued it will fail and that any suggestion it will remove small boat arrivals swiftly is “for the birds”.

He also publicly called for Britain to leave international treaties such as the European Convention on Human Rights in an article for the Telegraph that will be interpreted as a setting out of his stall for a future leadership contest.

Mr Sunak is fighting to convince Conservatives not to rebel in Tuesday’s crunch vote as he seeks to pass a new legislation in response to the Supreme Court ruling the Rwanda scheme is unlawful.

More moderate Tories are concerned about telling courts they must find that the East African nation is “safe”.

But some on the right want to go further in disapplying the European Convention on Human Rights. Both wings are seeking their own legal advice.

But the Times’s report states that asylum seekers will be able to lodge legal challenges against their deportation based on individual circumstances despite Mr Sunak’s Bill.

The advice was said to centre on the European court in Strasbourg blocking flights by granting an interim injunction as it did in June last year.

There appears to be disagreement over whether ignoring such injunctions would be a breach of the European Convention on Human Rights.

The advice from the Government Legal Department was said to have been signed off by top lawyer Sir James Eadie, who advocated for the Home Office in the Supreme Court case.

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Not disputing the advice, a Government official said: “We do not comment on or share Government legal advice and it would be very wrong for anyone recently departing Government to do so.

“Ministers are reassured that this Bill goes as far as it can within international law and therefore ensures we can get flights off to Rwanda next year.”

One source backed up the report, while another sought to argue the advice was just one of the opinions the Government had sought.

In an article for the Telegraph, Mr Jenrick said “some of the country’s finest legal minds” have determined that migrants will be able to lodge legal appeals against removal and that they could be “taken off flights in considerable number”.

“The idea, therefore, that this Bill will guarantee all those arriving are detained and swiftly removed is for the birds,” he wrote.

Mr Jenrick, who had long been allied to Mr Sunak before his resignation this week, argued that stopping Channel crossings would be easier “if we extricated ourselves from the complex web of international frameworks”.

Prime Minister Rishi Sunak during a press conference in the Downing Street Briefing Room
Prime Minister Rishi Sunak held a Downing Street press conference to defend his plan (James Manning/PA)

“It will only become painfully more apparent that these outdated treaties cannot be renegotiated any time soon, so they must give way,” he said.

Mr Jenrick also said that the Tories will be treated to “red-hot fury at the ballot box” unless they bring down current levels of legal immigration, which he argued makes integration “impossible”.

On Rwanda, the Prime Minister took the middle option by choosing to disapply parts of the Human Rights Act with his Bill rather than the European law which the right have been lobbying for.

The entire policy was attracting fresh criticism when it emerged that the UK had paid an additional £100 million on top of the £140 million already paid to Kigali.

Ministers are expected to pay another £50 million next year for the policy first announced in April last year but has so far been unsuccessful in removing a single migrant.

Failure to win Tuesday’s vote could plunge Mr Sunak’s leadership into a fresh crisis.

New legal migration minister Tom Pursglove suggested the Government could be open to compromises with would-be rebels.

A Home Office spokeswoman said: “The Government is committed to doing whatever it takes to stop the boats and get flights to Rwanda off the ground as soon as possible.

“Rwanda is ready to welcome large numbers of people relocated there. It is a safe country that cares deeply about supporting refugees and our Safety of Rwanda Bill will make this absolutely clear in UK law.”