Rishi Sunak has vowed to do “whatever it takes” to stop small boat crossings after the Supreme Court ruled his flagship policy of removing asylum seekers to Rwanda unlawful.

The Prime Minister insisted on Wednesday that his Government has spent the “last few months planning for all eventualities” as he comes under huge pressure to set out a Plan B.

Five justices at the UK’s highest court unanimously rejected the Government’s appeal over its policy of removing asylum seekers to the east African nation if they arrive by unauthorised means.

Expulsion flights to Kigali will stay grounded despite the UK handing over more than £140 million for a policy that has been stalled during more than a year of legal challenges.

Supreme Court President Lord Reed ruled there would be a risk of Rwanda returning genuine asylum seekers to face “ill treatment” in the country they had fled.

In a statement, Mr Sunak said: “We have seen today’s judgment and will now consider next steps.

“This was not the outcome we wanted, but we have spent the last few months planning for all eventualities and we remain completely committed to stopping the boats.”

He said that, “crucially”, the courts have ruled the “principle” of sending migrants to a third country is lawful.

“Illegal migration destroys lives and costs British taxpayers millions of pounds a year. We need to end it and we will do whatever it takes to do so,” he said.

He will face scrutiny at Prime Minister’s Questions before holding a Downing Street press conference on Wednesday afternoon.

Suella Braverman sacking
Suella Braverman warned there would be no ‘credible Plan B’ if the Supreme Court rejected the Government appeal (Andrew Matthews/PA)

After being sacked as home secretary this week, Suella Braverman said Mr Sunak had no “credible Plan B” if the Supreme Court rejected the Government appeal.

She alleged ministers will have “wasted a year” on the Illegal Migration Act “only to arrive back at square one” if they lose.

Mr Sunak is now expected to faces calls from Mrs Braverman and the Tory right to withdraw Britain from the European Convention on Human Rights.

But Lord Reed made it clear in his summary of the judgment that it is not the only international treaty relevant to the court’s decision, which also took into account domestic law.

New Home Secretary James Cleverly insisted the “bold and ambitious” Rwanda scheme is “just one part of a vehicle of measures to stop the boats and tackle illegal migration”.

Lord Reed agreed with the Court of Appeal decision earlier this year that there are “substantial” grounds to believe there is a “real risk” of refugees being returned to their home countries.

But he made it clear the judgment was only based on the current failure to “eliminate the risk” in Rwanda and said the changes needed to reduce this “may be delivered in the future”.

The flagship policy was first announced by Boris Johnson in April 2020 but not one migrant has been removed to Kigali during a series of legal challenges.

Campaigners welcomed the verdict, with the Freedom From Torture charity hailing it as a “victory for reason and compassion”.

Steve Smith, chief executive of the Care4Calais refugee charity, said: “The Supreme Court’s judgment is a victory for humanity.

“Today’s judgment should bring this shameful mark on the UK’s history to a close.”

Dover Tory MP Natalie Elphicke said a deal with France is now the best way to stop small boats crossing the English Channel, conceding the Rwanda policy is “effectively at an end”.

The rulings were based on evidence that Kigali has a “poor human rights record”, citing British police warning Rwandans in the UK of credible plans by the nation’s government to kill them.

Concerns of political and media freedom were also raised, as was the inability of the Rwandan courts to act independently of the government.

Evidence from the UNHCR, the United Nations’ refugee agency, cited Rwanda’s 100% rate of rejection of claims from countries in conflict zones such as Syria, Yemen and Afghanistan.

This is despite the UK authorities often finding the claims are “well-founded”.

The body also presented evidence of more than 100 cases of “refoulement” – the process of returning refugees to their origin countries – that have taken place after the UK agreed its deal with Rwanda.

Shadow home secretary Yvette Cooper said Mr Sunak’s “flagship policy has completely failed” as she accused him of failing to “have any serious plan to tackle dangerous boat crossings”.

“Labour argued from the start this plan is unworkable and extortionately expensive; now it has been confirmed as unlawful because the Government failed to ensure they had a robust and workable policy,” she said.

Downing Street has in recent days conceded that the policy is “crucial” to Mr Sunak’s promise to the nation of “stopping the boats”.

More than 27,300 migrants have been detected making unauthorised crossings of the English Channel so far this year, according to official figures

Whereas Mrs Braverman repeatedly signalled she wanted out of the ECHR, Mr Cleverly said, while foreign secretary in April, that he was “not convinced” the move is necessary.

He said the European countries that are not signatories to the Convention – Russia and Belarus – are a “small club”, adding: “I am not convinced it is a club we want to be part of.”