Orlin Rusev, 47, pleaded guilty before the trial on one count of conspiracy to spy for Russia after police found thousands of messages between him and Wirecard fugitive Jan Marselek, who led the group of Bulgarian citizens abroad.

Judge Nicholas Hilliard sentenced Rusev to 10 years and 8 months in prison, telling him that the operations he had led posed a serious threat to the UK's national security.

Rusev is one of six Bulgarians convicted for their involvement in the team led by Marsalek to monitor journalists, dissidents, and Ukrainian soldiers training at a US military base in Germany.

Three members of the group were convicted in March after a trial, while Rusev, his deputy Biser Dzhambezov, 44, and a third man, Ivan Stoyanov, 33, pleaded guilty last year.

Dzhambezov was sentenced to 10 years and 2 months.

Prosecutors said the team did not work directly for Russian intelligence and was motivated primarily by money.

The Russian embassy in London has not commented on the case, although the Kremlin has always rejected such espionage allegations.

Relations between Britain and Russia have deteriorated to levels not seen since the end of the Cold War, since the start of the war in Ukraine, with Britain accusing Russia of trying to provoke “chaos” in Europe.

Marsalek's lawyer in Germany, where he is wanted as the former chief operating officer of the bankrupt payment company Wirecard, previously declined to comment.

His whereabouts are unknown, but he is believed to be in Russia. | BGNES