A week ago, few westerners or Russians had heard of Alexander Litvinenko. Yet his gaunt and sallow face, splashed across newspapers this week, threatens to become a defining image of Vladimir Putin’s Russia. His deathbed charge that the Russian president was responsible for his demise may dog Mr Putin for the rest of his presidency and beyond.

Strangely, however, Mr Litvinenko was neither the Kremlin’s most damaging critic nor Russia’s most high-profile defector. And despite the alarming nature of the former KGB officer’s death – by poisoning with radioactive polonium-210 – intelligence experts say there is no concrete evidence Russian agents were involved, let alone Kremlin-sanctioned.