A controversial migration bill, spearheaded by British Prime Minister Rishi Sunak, is set to become law amid criticism from the United Nations.

The highly contested plan, which would make it easier to send asylum-seekers to Rwanda, is all set to become law after the government defeated attempts by parliament's upper house to make changes to the legislation.

The Illegal Migration Bill had been stuck in a battle between parliament's House of Commons and the House of Lords, Britain's unelected upper chamber, which had repeatedly made changes to the legislation to water it down.

In the early hours of Tuesday, the last of those proposed changes was voted down. It can now go for Royal Assent, where it is formally approved by the king and becomes law.

The plan to deport asylum-seekers has been criticized by some opposition politicians, lawyers, and civil rights groups as inhumane, cruel and ineffective.

United Nations human rights chief Volker Türk said Tuesday the bill's passage raises "very serious legal concerns" and sets "a worrying precedent for dismantling asylum-related obligations" that other countries may follow.

However, deportation flights to Rwanda are unlikely to start until next year at the earliest and will still hinge on a ruling by the Supreme Court on their legality later this year.

The new legislation is at the heart of the government's pledge to stop asylum-seekers from making the dangerous crossing from France to the southern coast of England on small, often unseaworthy boats.

It will prevent most people from claiming asylum in Britain without permission and will deport them either to their country of origin or a so-called safe country like Rwanda.

Among the amendments proposed and finally defeated in the Lords was a demand for shorter time limits on the detention of unaccompanied children, greater protections for victims of modern slavery, and six-month delays in the deportation of migrants.

Britain struck an initial 140-million-pound ($180 million) deal with the East African country last year but the policy has been tied up in the courts. The first planned Rwanda deportation flight was blocked a year ago in a last-minute ruling by the European Court of Human Rights.

The passage of the bill coincided with the arrival of a barge to house migrants off the southern coast of England. The government has defended the use of barges, insisting it is a cheaper alternative to hotels.

Last year, a record 45,755 people came to Britain in small boats across the Channel, mainly from France. More than 12,000 have arrived this year, a rate similar to 2022.

'Contrary to int'l law'

The United Nations, in the meanwhile, said the bill was at odds with London's obligations under international law.

The bill "is at variance with the country's obligations under international human rights and refugee law and will have profound consequences for people in need of international protection," the U.N. refugee and human rights chiefs said.

In a joint statement, they said the bill blocks access to asylum in Britain for anyone who arrives irregularly, having passed through a country – however briefly – where they did not face persecution.

The U.N. human rights chief Türk and the U.N. refugees head Filippo Grandi said the bill bars people from presenting refugee protection claims, whatever their circumstances, and creates sweeping new detention powers with limited judicial oversight.

"This new legislation significantly erodes the legal framework that has protected so many, exposing refugees to grave risks in breach of international law," Grandi said.

The 1951 Refugee Convention explicitly recognizes that refugees may be compelled to enter a country of asylum irregularly, the pair noted.

"I urge the U.K. government to renew this commitment to human rights by reversing this law and ensuring that the rights of all migrants, refugees and asylum-seekers are respected, protected and fulfilled, without discrimination," Türk said.