Britain's interior minister James Cleverly arrived in Rwanda on Tuesday to sign a new treaty that London hopes will revive controversial plans to transfer migrants to the east African country.

Cleverly's ruling Conservatives are trying to salvage their stalled bid to send asylum-seekers and other migrants to Rwanda after the UK Supreme Court last month blocked an earlier arrangement as unlawful.

The judges sided with a lower court decision that the policy was incompatible with Britain's international obligations because Kigali could forcibly return migrants to places where they could face persecution.

A major setback for Prime Minister Rishi Sunak who is under pressure to reduce immigration to Britain, he has vowed to persevere with the contentious project by securing the new treaty.

It will "address concerns" raised in the Supreme Court's ruling, and reportedly include commitments by Rwanda on the treatment of the migrants sent there.

Sunak's response also includes passing "emergency legislation" in parliament to designate Rwanda a safe country to end the "merry-go-round" of legal challenges.

"I'm fed up with our Rwanda policy being blocked," Sunak wrote in The Sun tabloid Tuesday.

"I've got the government working on emergency laws to end the merry-go-round so that we can fix this problem once and for all -- and stop the boats."

A UK-Rwanda migration "partnership" agreed in April last year envisaged sending to Kigali anyone who has made what London calls "dangerous or illegal journeys" to Britain on small boats from Europe or hidden in lorries.

The first deportees were aboard a plane to fly there in June 2022 when a last-minute European Court of Human Rights injunction prevented any deportations, prompting the further legal challenges.

The government insists the scheme is crucial to deter "illegal" immigration across the Channel from France on inflatable vessels -- an emotive issue set to feature prominently in a general election expected next year.

Nearly 30,000 have made the perilous journey this year -- down on the nearly 46,000 who crossed in 2022, but still far short of meeting Sunak's vow to "stop the boats".

Cleverly will sign the new treaty alongside Rwanda's Foreign Minister Vincent Biruta and "discuss key next steps" in their plan, according to his ministry.

"We are clear that Rwanda is a safe country, and we are working at pace to move forward with this partnership to stop the boats and save lives," Cleverly said in a statement ahead of the visit.

"The Supreme Court recognised that changes may be delivered in future to address the conclusions they reached -- and that is what we have set out to do together, with this new, internationally recognised treaty agreement."

While in Rwanda, Cleverly will also visit the genocide memorial in Kigali and staff at the British High Commission.