The British prime minister Rishi Sunak and his home secretary Suella Braverman – the first Punjabi and the latter Goan – suffered a devastating political blow on Thursday when judges ruled their vote winning plan to send illegal migrants to Rwanda in Africa was “illegal”.

Here in Britain, judges cannot be bought off by the government.

By two votes to one, three of Britain’s most senior judges in the Appeal Court overturned an earlier ruling by the High Court that the policy was legal and said that Rwanda is not a safe country.

Rishi realises that his chances of being re-elected at the next general election depends partly on whether he can be seen to be curbing illegal immigration.

He has said he wants to be judged on five pledges, including “Stop the boats”. The number of those who have landed on British beaches this year after crossing the channel on small dinghies has crossed 11,000. Last year, the number of illegal migrants – they included a substantial number of Indians – reached 45,755.

Suella, seen as being even more right wing than her Gujarati predecessor, Priti Patel, has been widely condemned by human rights groups for saying: “I would love to have a front page of the (Daily) Telegraph with a plane taking off to Rwanda. That’s my dream, it’s my obsession.”

Rishi announced he will seek to challenge the Appeal Court’s ruling in the Supreme Court.

To some it might seem ironic that two Indians, whose parents were immigrants themselves – of course, they point out that their mothers and fathers came legally via East Africa – are doing their best to keep out other migrants. In reality, any prime minister would have to tackle illegal trafficking.

Rishi declared: “While I respect the court I fundamentally disagree with their conclusions. I strongly believe the Rwandan government has provided the assurances necessary to ensure there is no real risk that asylum-seekers relocated under the Rwanda policy would be wrongly returned to third countries – something that the Lord Chief Justice (NB: one of the three Court of Appeal judges) agrees with.

“Rwanda is a safe country. The High Court agreed. The UNHCR have their own refugee scheme for Libyan refugees in Rwanda. We will now seek permission to appeal this decision to the Supreme Court.

“The policy of this government is very simple, it is this country – and your government – who should decide who comes here, not criminal gangs. And I will do whatever is necessary to make that happen.”

Labour gloated at Rishi’s comeuppance.

The party’s shadow home secretary, Yvette Cooper, said that the Tory policy to stop small boat crossings was “completely unravelling”.

“Ministers were forced to admit this week that it will cost £169,000 to send each person to Rwanda on top of the £140m of taxpayers’ money they have already spent,” she said. “The Rwanda scheme is unworkable, unethical and extortionate, a costly and damaging distraction from the urgent action the government should be taking.”

The archbishop of Canterbury, Justin Welby, has called the Rwanda policy “opposite the nature of God” and “un-Christian” and said it raised “serious ethical questions”.

The High Court ruling was challenged by 10 individual asylum seekers and the charity Asylum Aid.

They argued that the High Court “showed excessive deference” to the Home Office’s assessment that assurances made by the Rwandan authorities “provide a sufficient guarantee to protect relocated asylum seekers”.

Two of three judges – Sir Geoffrey Vos, the master of the rolls, and Lord justice Underhill – agreed that “deficiencies in the asylum system in Rwanda are such that there are substantial grounds for believing that there is a real risk that persons sent to Rwanda will be returned to their home countries”.

However, ministers could take heart from the fact that Lord Burnett, the Lord Chief Justice, dissented from the verdict, saying he believed Rwanda was a safe country.

Yolande Makolo, spokeswoman for the Rwandan government, said it “took issue” with the ruling.

“Rwanda is one of the safest countries in the world and we have been recognized by the UNHCR and other international institutions for our exemplary treatment of refugees,” she said.

Rishi has until July 6 to lodge a written appeal against the ruling. But the appeal court’s decision has significantly harmed his chances of winning the next election.