British Prime Minister Rishi Sunak said the government will appeal to the UK’s highest court after its proposal to deport asylum seekers to Rwanda was ruled illegal, a huge setback to his commitment to deter people entering in tiny boats.

Britain intended to transport tens of thousands of asylum seekers who arrived on British beaches more than 4,000 miles (6,400 km) to the East African country under an initial 140 million pound ($177 million) contract agreed last year.

The government argues the plan would smash the business model of human traffickers but critics say the policy is inhumane and will not work. On Thursday the Court of Appeal concluded by a majority of two to one that Rwanda could not be treated as a safe third country.

“While I respect the court I fundamentally disagree with their conclusions,” Sunak said in a statement, adding the government would seek to overturn the decision in the UK 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,” he added. “And I will do whatever is necessary to make that happen.”

The ruling comes as a huge blow for Sunak as he grapples with high inflation, rising interest rates and declining public support amid growing pressure from his party and the public to tackle rising numbers of asylum seekers costing 3 billion pounds a year to accommodate.

Sunak has made “stop the boats” one of his five top priorities, and hopes a fall in arrivals might help his Conservative Party, trailing by about 20 points in opinion polls, pull off an unexpected win at the next national election.

The first planned Rwanda deportation flight was blocked a year ago in a last-minute ruling by the European Court of Human Rights (ECHR), which imposed an injunction preventing any deportations until the conclusion of legal action in Britain.

In December, the High Court ruled the policy was lawful, but that decision was challenged by asylum seekers from several countries such as Syria, Iraq and Iran, along with human rights organisations.