Legal challenges are being prepared against the United Kingdom government's migrant deportation policies as lawyers seek to overturn returns to Bulgaria, citing reports of mistreatment of migrants and asylum-seekers within the country.

UK Prime Minister Keir Starmer said earlier this week that unchecked immigration threatened to turn the UK into "an island of strangers" and had already inflicted "incalculable" harm on the country.

Starmer made the comments as he presented the government's latest immigration white paper on Monday that outlines tougher citizenship rules, including enhanced English language requirements. The measures aim to reduce net migration to about 240,000 annually by 2028. It now stands at 728,000.

According to government figures, more than 24,000 individuals have been returned from the UK through both voluntary and forced departures since the Labour government took power in July. Of those, more than 200 were deported to Bulgaria last year.

Through informal agreements with several nations, the UK can deport asylum-seekers back to countries where they first entered European territory.

Violation cited

Lawyers are contesting deportations to Bulgaria from both the UK and European Union member states, saying returnees face treatment that may violate Article 3 of the European Convention on Human Rights.

Allegations include Bulgarian authorities ignoring emergency calls to rescue three Egyptian teenagers, who later died in freezing conditions near the border with Turkiye, The Guardian reported.

Multiple testimonies, including those collected by humanitarian groups, reveal threats of detention and alleged violence used to force migrants back to their countries of origin — claims that Bulgarian authorities deny.

Several Syrians are challenging their deportation to Bulgaria through UK courts, according to George Sheldon Grun, a public-law caseworker at Duncan Lewis Solicitors.

"The UK government considers Bulgaria a safe country for return, but the reality for those removed suggests otherwise," the lawyer said.

A UK government spokesperson said: "As the public rightly expects, anyone unlawfully in the UK with refugee status in another country will be removed and returned back to that country if deemed safe to do so."