One British intelligence source said: “This marked a blatant return to the bad old days of the cold war when the KGB thought it could act with impunity anywhere it pleased.”

These so-called “Hunter-Killer” powers also curtailed the right of the Russian media - already cowed and under the control of the Kremlin - to report on these operations. However, the enactment of these new laws only put on a legal footing powers which Russian intelligence had been using extra-judicially for years.

In Chechnya, the assassination of enemies of Russia is now so common that it scarcely bears comment, and in 2004 two Russian agents were arrested and sentenced to death in Qatar for the killing of exiled Chechen separatist leader Zelimkhan Yandarbiyev. The Russian team hunted him down and planted a bomb in his car. The Qatari court ruled that the killing was sanctioned by “the Russian leadership”. The men were not executed but sent back to Russia following promises from the Kremlin that they would be imprisoned. Rumour has it that they were decorated for the assassination operation.

Akhmed Zakayev, a friend of Alexander Litvinenko and a former field commander in the first Chechen war who later became the deputy prime minister of Chechnya, says the killing of Litvinenko proved to the British people that Putin was “destroying democratic freedoms in Russia and beyond”.

Mackay also draws attention to a disturbing aspect of the Zakayev extradition case that has not been widely covered in international media:

One UK source closely linked to British intelligence told how he had a conversation with a Russian intelligence officer in 2004, in which the Russian spy spoke of the killing of a British citizen carried out by Russian agents. In January 2004, Lieutenant-Colonel Robert Workman was found shot dead on his doorstep in the Hertfordshire hamlet of Furneux Pelham. The killing seemed completely motiveless.

However, the Russian intelligence source told his British contact that Robert Workman was killed in a case of mistaken identity. The real target had been a judge called Timothy Workman who lived not far from the scene of the murder.

In late 2003, Judge Workman infuriated the Kremlin when he rejected Russia’s extradition request for Akhmed Zakayev, the Chechen leader in London. Workman said that Zakayev faced a “substantial risk” of being tortured if he was returned to Moscow to stand trial. The Kremlin accused Workman of playing “cold war politics”.

Also in 2003, Judge Workman called a halt to Russia’s attempt to have Boris Berezovsky extradited from Britain. The billionaire oligarch had fallen out with Putin and has bitterly criticised the ruling regime. Berezovsky was also a close friend of Alexander Litvinenko.