Some asylum seekers will be flown to Rwanda to have their applications processed, under UK government plans.
Boris Johnson is set to unveil the plans later, before Home Secretary Priti Patel signs a migration deal with the African nation.
BBC home editor Mark Easton said the trial scheme would mean single men arriving in Britain via Channel crossings could be forcibly removed.
Refugee organisations have criticised the plans as cruel and urged a rethink.
Labour said the plan was “unworkable, unethical and extortionate” – and one designed to “distract” from Mr Johnson’s fine for breaking Covid-19 laws.
The Liberal Democrats said the proposal would be expensive and ineffective.
The deal is expected to see Rwanda, which is part of the Commonwealth, given an initial £120m as part of a trial, but opponents say the annual cost of the full scheme would be far higher.
In a speech in Kent, Mr Johnson will argue that action is needed to stop “vile people smugglers” turning the ocean into a “watery graveyard”.
Last year, 28,526 people are known to have crossed the English Channel in small boats, up from 8,404 in 2020.
Around 600 people made the crossing on Wednesday, and Mr Johnson will say the figure could reach 1,000 a day within weeks.
“We cannot sustain a parallel illegal system,” he will say. “Our compassion may be infinite, but our capacity to help people is not.”
Precise details of the policy are yet to be confirmed.
The prime minister will announce plans to hand operational control of the Channel to the navy, break the business model of people-smuggling gangs, and deter people from risking the crossing.
The measures are part of the government’s long-term plan to “take back control of illegal immigration” after Brexit, Mr Johnson will say.
While the number of people crossing the Channel in boats has increased, last year saw fewer people using other routes – such as by lorry – in part because of increased security at the Port of Calais.