LONDON - British Prime Minister Keir Starmer and French President Emmanuel Macron will announce tougher migration controls on Thursday, capping a state visit designed to deepen ties, including in defense and nuclear cooperation.

After hosting Macron for a three-day visit that included a carriage procession to Windsor Castle with King Charles and a state banquet, Starmer wants Macron to deliver on his promise of greater "cooperation and tangible results" on migration.

Starmer, who has faced challenges to his popularity since his election landslide last year, is working to address high levels of immigration, including asylum seekers arriving by small boats, to try to stem the growing influence of the Reform UK party, led by Brexit campaigner Nigel Farage.

READ MORE: UK, France to speed up efforts to tackle small boat crossings

A British government source said Britain and France had agreed a deal on a "one in, one out" migrant returns scheme - which would see Britain deporting to France undocumented people arriving in small boats, in return for an equal number of legitimate asylum seekers with UK family connections.

The government source said it would initially be limited, but could be scaled up. Local media reported that Britain would send back 2,600 people a year, a fraction of the more than 35,000 arrivals reported by the government last year.

More than 21,000 people have arrived on small boats this year, a record number.

"On small boats, we have now the understanding and acceptance that this is a shared challenge for the first time. We're working together closely for the first time," defense minister John Healey told BBC News.

'Migration pull factors'

The importance of the deal will likely be highlighted by Starmer, who, like Macron, is facing domestic woes, but it was not clear whether the agreement would come with conditions or have a big enough impact.

The policy, which is similar to a scheme used by the EU and Türkiye, carries risks for Macron from his right-wing political critics who may question why he has agreed to take back migrants wanting to live in Britain.

Macron had also called on Britain to address "migration pull factors," suggesting that it should be harder for migrants in Britain to find work without legal residential status.

On Wednesday, Starmer's office said the British leader had told Macron Britain was increasingly arresting undocumented workers to deter them from coming to Britain for jobs.

READ MORE: British PM recalibrates ties with EU, seeking more consensus

Underlining closer ties between the two countries since Britain left the European Union (EU) in 2020, the two leaders will strengthen their defense ties.

"As close partners and NATO allies, the UK and France have a deep history of defense collaboration and today's agreements take our partnership to the next level," Starmer said in a statement. "We stand ready to use our shared might to advance our joint capabilities."

An official of Elysee Palace, the residence of the French president, said: "We are providing capabilities to Europeans in the face of these increased threats, and in the nuclear field, we are strengthening our solidarity and the anchor of our two countries."