Sir Keir Starmer has been warned his migrant "returns hubs" could be hijacked by Russian spies.

Security advice from the intelligence service suggested the Balkans, which is being earmarked as a prime location the hubs, is unsafe for migrant deportation schemes because of its proximity to Russia.

The advice privately warned that the proposals would mean creating sensitive national infrastructure and facilities in "a Russian sphere of influence" that could be infiltrated and targeted by agents working on behalf of the Kremlin, The Times has revealed.

Migrants sent to the region could also be targeted and exploited by Vladimir Putin's regime, the advice added.

Vladimir Putin

Earlier this month, the Prime Minister confirmed that the Government was in talks with "a number of countries" about return hubs, which he described as "a really important innovation".

Serbia, Kosovo, North Macedonia and Bosnia-Herzegovina are on a shortlist of about nine countries drawn up by ministers and officials as potential destinations to which rejected asylum seekers would be sent after all avenues of appeal have been exhausted in the UK.

Albania had also been on the list but was its Prime Minister, Edi Rama, ruled out such an arrangement.

A plan for offshore migrant hubs in the Balkans was blocked in light of MI6 concerns when the previous Conservative Government drew up a shortlist of countries for a Rwanda-style deportation scheme in 2022.

Sir Keir Starmer

Separate security sources have said that the same concerns have been raised in response to Starmer's efforts to open return hubs in the region.

A Government source who was briefed by security officials warning against the Balkans region told The Times: "The advice we got was you'd be sending people into a Russian sphere of interest."

"They cited critical UK national infrastructure, facilities and systems that would be set up that could be infiltrated by the Russians by installing agents and other personnel working in the interest of the Kremlin," the source continued. "You'd be planting a prime bit of British interest, British real estate, right into an area where Russia has the ability to control and influence much more than other areas in the world."

Sources also pointed out that Serbian President Aleksandar Vucic is a close ally of Putin. He has visited Moscow several times in the past year, most recently when he attended Russia's Victory Day parade in Red Square.

Albania's Prime Minister Edi Rama

Another reason cited by security officials were rules allowing Russian citizens and passport holders to move freely in and out of Serbia. Britain began informal talks over return hubs with several countries, including Kosovo, this week.

Kosovan President Vjosa Osmani said her country would be "open" to talks over a potential deal to take Britain's failed asylum seekers. However, experts have warned about the legal hurdles given that several European countries do not recognise the nation's independence and because it is not a signatory to the European Convention on Human Rights.

Downing Street is understood to have set a target to announce return hub destinations by the time Britain hosts a meeting of western Balkan leaders in London in the autumn, where illegal migration will be top of the agenda.

However, there is increasing frustration at the centre of Government over the lack of progress made by the Home Office on what form it wants return hubs to take.

The Foreign Office said it would not provide a "running commentary" on the plans to open migrant return hubs and declined to comment further.