LONDON (AP) — Britain’s Supreme Court ruled Wednesday that the government’s contentious plan to send some migrants on a one-way trip to Rwanda is illegal, striking a major blow to a key policy of Prime Minister Rishi Sunak’s government that has drawn international attention and criticism.

Five justices on the country’s top court ruled unanimously that asylum-seekers sent to Rwanda would be “at real risk of ill-treatment” because they could be returned to the home countries they’d fled.

Sunak, who has pledged to stop migrants reaching Britain in small boats across the English Channel, said the ruling “was not the outcome we wanted.”

But he added, “we have spent the last few months planning for all eventualities and we remain completely committed to stopping the boats.”

Refugee and human rights groups welcomed the decision. Charity ActionAid United Kingdom (UK) called it a vindication of “British values of compassion and dignity.” Amnesty International urged the British government to “draw a line under a disgraceful chapter in the UK’s political history.”

Britain and Rwanda signed a deal in April 2022 to send some migrants who arrive in the UK as stowaways or in boats to the East African country, where their asylum claims would be processed and, if successful, they would stay.

Britain’s government argued that the Rwanda policy would deter people from risking their lives crossing one of the world’s busiest shipping lanes, and would break the business model of people-smuggling gangs. Opposition politicians, refugee groups and human rights organisations said the plan was unethical and unworkable.

No one has yet been sent to the country as the plan was challenged in the courts.

Reading the unanimous decision, President of the Supreme Court Robert Reed said Rwanda could not be relied on to keep its promises not to mistreat asylum-seekers sent from Britain.

He cited the country’s poor human rights record, including enforced disappearances and torture, and said Rwanda practiced “refoulement” – sending migrants back to unsafe home countries.

The judges concluded there were “substantial grounds for believing that asylum-seekers would face a real risk of ill-treatment by reason of refoulement in the event that they were removed to Rwanda.”

The UK government has argued that while Rwanda was the site of a genocide that killed more than 800,000 people in 1994, the country has since built a reputation for stability and economic progress.

Critics say that stability comes at the cost of political repression. The court’s judgement noted multiple rights breaches, including political killings that had led UK police “to warn Rwandan nationals living in Britain of credible plans to kill them on the part of that state.” They said Rwanda has a 100 per cent rejection record for asylum-seekers from war-torn countries including Syria, Yemen and Afghanistan.

“The evidence establishes substantial grounds for believing that there is a real risk that asylum claims will not be determined properly, and that asylum-seekers will in consequence be at risk of being returned directly or indirectly to their country of origin,” the judges said. “In that event, genuine refugees will face a real risk of ill-treatment in circumstances where they should not have been returned at all.”

The ruling leaves in tatters a policy that has cost the British government at least 140 million pounds ($175 million) in payments to Rwanda, without anyone being sent to that country. The first deportation flight was stopped at the last minute in June 2022, when the European Court of Human Rights intervened.

In December, the High Court in London ruled that the Rwanda plan is legal, but that the government must consider the individual circumstances of each case before putting anyone on a plane.

The Court of Appeal in June backed a challenge by asylum-seekers from countries including Syria, Vietnam and Iran. The court ruled that the plan was unlawful because Rwanda is not a “safe third country.”

That was challenged at the Supreme Court by the government, which argued at a hearing last month that it had thoroughly assessed the risks and would ensure that Rwanda’s government abides by its agreement to protect migrants’ rights.