Prime Minister Rishi Sunak’s government wants to send thousands of migrants more than 4,000 miles (6,400 km) away to Rwanda as part of a 140 million pound ($174 million) deal agreed last year.

It regards the plan as central to deterring record numbers of asylum seekers arriving in small boats across the Channel from France, something Sunak has made one of his five priorities, facing pressure from some of his own Conservative lawmakers and the public to resolve the issue.

However, the first planned flight to Rwanda last June was blocked by a last-minute ruling by the European Court of Human Rights, which imposed an injunction preventing any deportations until the conclusion of legal action in Britain.

In December, the High Court in London ruled the policy was lawful, but that decision is being challenged by asylum seekers from countries including Syria, Sudan, Iraq, Iran and Vietnam along with some human rights organizations.

Their lawyers say the government’s argument that Rwanda is a “safe third country” is flawed.

Raza Husain, one of their lawyers, told the Court of Appeal at the start of a four-day hearing that Rwanda was an authoritarian one-party state that did not tolerate opposition and imprisons, tortures and murders opponents.

“There will only be any form of deterrent effect if a third country to which asylum seekers are removed is one to which they would not wish to go,” Husain said, arguing the government had failed to tread the line between deterring migrants and remaining within Britain’s human rights obligations.

However, lawyers representing the British government stressed that its deal with Rwanda is “subject to an exacting set of monitoring arrangements”, including by the UN High Commissioner for Refugees, who has intervened in the appeal.

They said in court filings that evidence about Rwanda’s asylum system was of little relevance as it had no bearing on how asylum seekers would be dealt with under the deal with Britain.

Rwanda says migrants will be treated with respect and dignity and the deal will offer them better opportunities.

Ian Burnett, the Lord Chief Justice and one of three judges hearing the case, said the issue of the safety of Rwanda would be the core issue.

In March, the government announced it would bring in a new law which would bar anyone who arrived in a small boat from claiming asylum and see them deported back to their homeland or a safe third country.

Sunak and his ministers argue that this would break the business model of people traffickers, but critics say it is impractical, immoral and will not work.

More than 45,000 migrants arrived in small boats on the English south coast in 2022, a record number, and in court documents last week, the government said it was anticipating as many as 56,000 would cross the Channel this year.

Faced with a backlog of claims, more than 100,000 asylum seekers are being accommodated by the government with about 50,000 in hotels at a cost of 6.2 million pounds ($7.7 million)per day.