Prime Minister Rishi Sunak said on Monday his plan to stop migrants arriving in Britain in small boats had reduced crossings by 20%, an update he hopes will ease criticism from his party and in the country over immigration policy.

Sunak, who is expected to lead his governing Conservative Party into a national election next year, has promised to "stop the boats" as one of his five pledges to Britain after he was propelled to power in October last year.

But he has been criticised by members of his own party and the public for not moving quickly enough, with people protesting about the housing of migrants in hotels after a record number arrived in Britain last year.

"In the five months since I launched the plan, crossings (across the English Channel) are now down 20% compared to last year," Sunak told a news conference in southern England.

"The plan is working," he said, adding his government was not complacent and would work hard to make sure parliament passed a new law.

He also said a deal with Albania had meant that Britain was returning more migrants to the country.

"We've now returned 1,800 to Albania in just six months. We've gone from accepting around one in five Albanian asylum cases, to now just one in 50," Sunak said.

"So far this year, the number of Albanian small boat arrivals has fallen by almost 90%."