Officers began detaining potential deportees on Monday at their homes or as they came to report at immigration centres – even though the first flights are not due to depart for at least another nine weeks.

British authorities have started to detain migrants in preparation for them to be sent to Rwanda under the European country’s new immigration policy, the government said on Wednesday.

The announcement came after the parliament approved last month British Prime Minister Rishi Sunak’s flagship immigration law that allows asylum-seekers who arrive in Britain without permission to be deported to so-called safe third countries.

The law dodged a 2023 Supreme Court ruling that prohibited sending migrants to Rwanda because it “would expose them to a real risk of ill-treatment”. Rwanda – which has a population of 13 million – claims to be one of the most stable countries in Africa, but human rights groups routinely criticise the government for restricting free speech.

The UK government said Wednesday that it booked commercial charter planes and increased detention capacity to more than 2,200 spaces in preparation for the first Rwanda-bound flights. Sunak said Monday that flights should begin within 10 to 12 weeks, and his spokesperson said the prime minister was pleased that “the first detentions have taken place”.

Images released by Britain’s interior ministry on Wednesday showed a man being put in a van by immigration enforcement officials, and another being led out of his house in handcuffs.

“Our dedicated enforcement teams are working at pace to swiftly detain those who have no right to be here so we can get flights off the ground,” Interior Minister James Cleverly said in a statement.

Officials have refused to say how many people had been held so far, but sources said there had been “dozens” of detentions across the UK, in cities including Glasgow, Liverpool, Birmingham, and Bristol. Enforcement action is said to have taken place in England, Wales, Scotland, and Northern Ireland.

Care4Calais, a refugee charity, said the detentions had started on Monday.

A spokesperson said the group’s helpline had received calls from “tens of people”, adding that they still did not know who would be earmarked for the first deportation flight, or when it would be attempted.

The government expects to deport 5,700 migrants to Rwanda this year, a senior minister said Tuesday. Of those, 2,143 “can be located for detention,” the ministry said, leaving more than 3,500 migrants unaccounted for. Ministers said the enforcement teams would find them.

More than 7,500 migrants have arrived in England on small boats from France so far this year. Sunak’s ruling Conservative Party says the new law will deter people from making the perilous trip across the English Channel. Five people died trying to cross the channel last week.

Labor opposition members have dismissed the deportation policy as a “gimmick” that will not deter cross-channel arrivals, and some public resistance to deportations remains.

The FDA, a trade union representing civil servants who may be instructed to help enact the new policy, said it had launched a legal challenge because its members were potentially being asked to breach their governing code.

“Civil servants should never be left in a position where they are conflicted between the instructions of ministers and adhering to the Civil Service Code, yet that is exactly what the government has chosen to do,” FDA General Secretary Dave Penman said.

Other unions and human rights charities opposed to the policy are expected to launch challenges to stop the flights from taking off after the UK Supreme Court declared the policy unlawful last year.