London and Paris unveiled a "pilot" programme on Thursday to return to France some of the migrants arriving in the UK on small boats across the Channel, as President Emmanuel Macron wrapped up his state visit.

Prime Minister Keir Starmer called the deal, hammered out during the French leader's three-day visit, "groundbreaking" and capable of stemming the record numbers of people who have embarked on the perilous journey so far this year.

"This is groundbreaking, because this is a scheme intended to break the model, and to make it clear that if you cross in a small boat, then you'll end up where you started," he said in a joint press conference with Macron.

"In exchange for every return, a different individual will be allowed to come here" in a safe manner, Starmer said, adding that the scheme would start within "the coming weeks".

Although Starmer did not say how many people might be returned to France, media reports suggest it could initially total around 50 people a week.

In comments likely to infuriate pro-Brexit groups, Macron said Britain's 2020 departure from the EU had worsened the situation in the Channel, cutting off legal migration routes and access to the bloc's own returns agreements.

"So for people wanting to cross, there is no legal way, nor a way of sending people back after a crossing," Macron said.

"This is a pull factor to attempt the crossing - exactly the inverse effect of what Brexit promised."

RTHK's UK correspondent, Gavin Grey, said it was not immediately know which type of migrants would qualify for the scheme, or how many will be let in.

"There is a rumour that it could be up to 50 people a week. That might sound a lot, but we are getting thousands crossing the English Channel every week," he told RTHK's Hong Kong Today programme.

"More than 170,000 have arrived in small boats since 2018, when figures began to be gathered. This year so far, the five and a bit months so far, have seen nearly 20,000 arrive in these first six months. And that is 50 percent up on the previous year. So the idea that it might be 50 a month, it's pretty insignificant."

Alongside migration, the two leaders used the visit to work on a raft of initiatives and shared concerns over defence, trade and culture.

They included addressing the volatile situation in the Middle East, continued support for Ukraine and a "reboot" of defence ties, including joint missile development and nuclear cooperation. (AFP)