The UK-French "one-in, one-out" pilot plan has come into force, aimed to deter the number of small boats crossing the English Channel.
The scheme will see some of those arriving in the UK detained and returned to France, and in exchange, the UK will accept the same number of asylum seekers.
Providing they have not already tried to make the crossing and can pass eligibility checks, the plan will "deliver real results," according to Sir Keir Starmer.
The prime minister and French President Emmanuel Macron announced the agreement in July which is a "product of months of grown-up diplomacy."
The government is yet to confirm the number of migrants that would be returned and accepted, but said it would look to "ramp up both the pace and scale of returns over the course of the pilot scheme."