HASTINGS, England - Mussadiq was at his hotel in this seaside town when he received the letter threatening to deport him to Rwanda.

The three-page missive said Britain's Home Office wouldn't even consider the substance of his asylum claim before exhausting whether he could be sent to another country, including the central African nation with which it has a new deal.

"I risked my life to come here," said Mussadiq, 27, who fled Afghanistan after he was forced to fight for the Taliban. He crossed the English Channel in a small boat, overcrowded with migrants, which sprung a leak along the way and required a coast guard rescue. Like other migrants interviewed for this article, he spoke on the condition that his last name be withheld, in the interest of protecting his asylum chances.

But his hopes for a less precarious life have run up against Prime Minister Rishi Sunak's pledge to "stop the boats" and a new asylum policy that places Britain on the extreme end of the spectrum in Europe - and aspires to something like Australia's mandatory detention and offshoring.

The United Kingdom's Illegal Migration Act 2023 - passed by Parliament and granted royal assent last month - effectively bans those who enter Britain via unofficial means from applying for asylum here. The law places a legal duty on officials to detain and deport people back to their birth country, if that's possible, or to a "safe third country," including Rwanda, where their asylum claims can be processed. Once relocated, asylum seekers would be barred from ever entering Britain again.

"It is this country, and your government, who should decide who comes here, and not criminal gangs," Sunak said at a news conference.

In its essence, what Britain is trying to do is an outgrowth of Brexit, driven by a desire to "take back control" of the borders. But beyond the British particulars, the effort has captured the interest of other nations that would similarly like to outsource the issue of migration.

"A lot of other countries are watching the U.K. experiment closely, and they are hoping it succeeds," said Jeff Crisp, an associate fellow at the Chatham House think tank.

The United Nations was alarmed enough to issue an unusual statement, saying that Britain was at odds with international law and was setting "a worrying precedent for dismantling asylum-related obligations that other countries, including in Europe, may be tempted to follow."

The U.K. approach is "a blanket removal process, enshrined in law, basically removing [asylum seekers] without adequate examination of the merits of the case. It's quite brazen," said Nadia Hardman, a researcher in the refugee and migrants rights division of Human Rights Watch.

Within Britain, the tough line on migration goes over well with the pro-Brexit base and other key voting target groups of the ruling Conservative Party. Nearly 60 percent of Conservative voters say immigration is one of the most important issues facing the country, according to YouGov surveys. So Sunak's government is trying to show it can make headway on the issue before the next election, expected next year.

Voters are also focused on a cost-of-living crisis - which economists say has been driven by Brexit. So the government has framed the migration issue as an economic issue, too, regularly noting that the public is paying nearly $7.6 million a day to put asylum seekers up in hotels.

In a highly symbolic move billed as a cost-saving measure, the government retrofitted a giant, hulking barge called the Bibby Stockholm to house 500 migrants. But the effort to rehouse migrants on the barge has been beset with problems. After a series of delays, on Monday, a small group moved onboard. Amid criticism of the arrangement, Lee Anderson, the deputy chair of the Conservative Party, said Tuesday that migrants who don't want to live on a barge could go "back to France," using an obscenity. On Friday, the vessel was being evacuated over health concerns.

A further aspect of Brexit is influencing Britain's asylum approach. Since leaving the European Union, Britain can no longer legally return asylum seekers to the first E.U. country they entered. Rwanda - which agreed to take 1,000 people over the first five years of a pilot project - is the only "safe third country" with which the U.K. has a deal.

The legality of that arrangement, however, is in doubt after an appeals court ruled that Rwanda should not be considered a safe country where asylum claims would be fairly processed. The British government is appealing to the Supreme Court.

Sonia Lenegan, an immigration lawyer, said the letters mentioning Rwanda that some migrants are receiving are intended "mainly to terrify. . . . In practice, no one is going to Rwanda anytime soon."

Deportation flights are not expected before next year, at the earliest.

If third-country deportations ultimately go forward, though, they would be a big deal - impacting not only the lives of asylum seekers but the global framework for refugees.

Crisp of Chatham House noted that Britain was one of the original signatories of the 1951 Refugee Convention. If the U.K. "is able to dump its refugees on another country, what message does it send to the world's least-developed and poorest nations, who already bear the brunt of the refugee burden? The whole international refugee system is based on the notion of cooperation," he said.

Britain is far from the only country trying to make migration someone else's issue. The E.U. has effectively adopted a "fortress Europe" mentality and sought various ways to block migrants well beyond its borders. It helped build up the Libyan coast guard to intercept migrants in the Mediterranean. It recently signed a deal with Tunisia, offering millions in return for help stopping migrants from making the journey to Europe. And it has indicated to Balkan countries that their E.U. candidacy will be influenced by their ability to curtail migration along the "Balkan route."

"Europeans are effectively bribing third countries to help better manage the problems they are having with migrants," said Mujtaba Rahman, an analyst with Eurasia Group.

But while the E.U. has talked about establishing asylum processing centers in North Africa, and Denmark at one point signed a deal with Rwanda on the possible transfer of asylum seekers, those plans didn't get very far.

Britain would set the precedent.

"Very few countries take the U.K.'s extreme stance," said David Cantor, director of the Refugee Law Initiative at the University of London. "In some ways, it goes further now even than Australia. Perhaps the closest parallels are with the ways that countries like North Korea or Bhutan treat the refugee issue."

Cantor said the British plan is vastly more severe than the Biden administration's asylum policy, which is also caught up in legal challenges.

"The U.S. functions as a carrot-and-stick approach. The U.K. has no carrot, just a stick," Cantor said.

The Biden administration has said those who don't follow the rules and enter the United States illegally could face deportation or criminal prosecution. The administration has also been working to set up remote asylum processing centers in Colombia and Guatemala. But the idea, Cantor said, is to give people who fulfill the criteria a "direct, safe and legal pathway" to asylum in the United States, allowing them to avoid long and dangerous journeys on smuggling routes.

Britain isn't offering legal pathways of that sort, he said.

Sunak insists that Britain remains a "compassionate and generous country." He notes that it has offered special visas to Ukrainian refugees and Hong Kongers fleeing political persecution. But he says the system is overwhelmed by people who aren't "genuine refugees."

"People must know that if they come here illegally, it will result in their detention and swift removal," he said. "Once this happens, and they know it will happen, they will not come, and the boats will stop."

Refugee advocacy groups say Britain is facing a manufactured crisis.

Yes, channel crossings are on the rise. Last year, more than 45,000 people came to Britain in small boats - a huge increase from the 300 who did so in 2018. But Britain received far fewer asylum applications than Germany or France. And, when comparing numbers of applicants as a proportion of population, Oxford's Migration Observatory found that in 2021, the latest figures, Britain ranked 19th in Europe.

Refugee advocates say that if the cost of housing people is the concern, Britain could save money by clearing its unnecessary backlog of applications.

Instead, asylum seekers are being kept in a state of limbo.

Many of those interviewed outside a hotel in Hastings said they were hoping to settle in Britain because they had family there, or saw their best chances in an English-speaking country, and that the government's new policies were not a deterrent - but were frightening.

Bidias, 32, from Cameroon, said he found himself poring over news reports on the government's latest efforts.

"The barge looks like a jail . . . and I can't go back to Africa," he said. "We came here knowing England was a safe country, that we could find some help here. We are surprised by all of this."

The Washington Post's Emily Rauhala in Brussels contributed to this report.