The Prime Minister was resisting pressure from some Conservatives to quit the European Convention on Human Rights (ECHR) but hinted he could change UK laws “if necessary” and may reconsider “international relationships”.
Sacked home secretary Suella Braverman demanded on Wednesday that Mr Sunak introduces “emergency legislation” blocking off the ECHR, Human Rights Act and other routes of legal challenge.
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.
Downing Street was unable to say whether the expulsion flights to Kigali that have been grounded for more than a year during the legal challenges will take off before the next election.
None of the £140 million the UK has already paid to Rwanda can be clawed back as the new treaty is expected to add even more to the costs as negotiations are under way.
New Home Secretary James Cleverly said the Rwanda deal would be increased to a legally-binding treaty “as soon as possible” to alleviate the concerns to make it consistent with international law.
To alleviate the Supreme Court’s concerns that Rwanda could send genuine refugees back to the countries they have fled, he said new plans being drawn up mean that anyone removed to Kigali cannot be “sent to another country than the UK”.
Labour leader Sir Keir Starmer demanded an apology to the nation from Mr Sunak for wasting millions of pounds of taxpayers’ cash on the “ridiculous, pathetic spectacle”.
The Prime Minister vowed to do “whatever it takes” to end Channel crossings, as he set out how the first step will be to “finalise” a new treaty with Rwanda.
He focused on the Supreme Court suggesting changes there to prevent genuine asylum seekers being sent back to the countries they have fled could render the plans lawful.
“There are further elements that they want additional certainty on and noted that changes can be delivered in the future to address those issues,” Mr Sunak said at Prime Minister’s Questions.
“The Government has been working already on a new treaty with Rwanda and we will finalise that in light of today’s judgment.”
But he dangled an offer to the Tory right by suggesting he could go further, as sacked home secretary Mrs Braverman waited in the wings to challenge his authority.
“If it becomes clear that our domestic legal frameworks or international conventions are still frustrating the plans at that point, I am prepared to change our laws and revisit those international relationships,” the Prime Minister said.
“The British people expect us to do whatever it takes to stop the boats and that is precisely what this Government will deliver.”
Mrs Braverman demanded that the Prime Minister changes the law to prevent legal challenges, arguing there is “no chance of curbing illegal migration within the current legal framework”.
“We must legislate or admit defeat,” she wrote on social media.
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.
Mrs Braverman said after her ousting this week that Mr Sunak had no “credible plan B” and would be “back at square one” in the event of legal failure, as she took aim at his approach to the ECHR.
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.
In the Commons, Mr Cleverly said that in the last few months, ministers have been working with Rwanda to “provide the certainty that the court demands”.
“We have been working with Rwanda to build capacity and amend agreements with Rwanda to make clear that those sent there cannot be sent to another country than the UK,” he said.
The Home Secretary told former prime minister Theresa May she made an “incredibly important point” when she said the ruling on Rwanda came “regardless of the ECHR”.
Mr Sunak told Rwandan president Paul Kagame in a call that he remains firmly committed to their asylum partnership.
Boris Johnson urged the Prime Minister to change the law to designate Rwanda a “safe” country, arguing it is the “only one way to end the legal blockade on Rwanda”.
Mr Sunak will hold a Downing Street press conference on Wednesday afternoon as his more hardline MPs grow increasingly frustrated at his leadership.
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 by Rwanda to their home countries.
But he made it clear the judgment was based only on the current failure to “eliminate the risk” there and said the changes needed to reduce this “may be delivered in the future”.
The Supreme Court’s ruling, though, made clear the challenges ministers must overcome, saying there was “evidence of a culture within Rwanda of, at best, inadequate understanding of Rwanda’s obligations under the Refugee Convention”.
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.”
The legal 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.
More than 27,300 migrants have been detected making unauthorised crossings of the English Channel so far this year, according to official figures.