On April 23, 2002, Alexander Litvinenko, a former officer of the Russian secret service, arrived at Heathrow, supposedly on a stopover before flying on to the Caribbean. Claiming that he was being persecuted by the Russian authorities, he sought political asylum.

Alexander Valterovich Litvinenko was born in 1962 in Voronezh, south of Moscow. After high school and extended service in the Soviet Army (in which his grandfather was an officer), he graduated from the Interior Forces Military Academy, joining the KGB in 1988.

While his early career was in espionage, by 1991 he had made a name for himself in the organised crime and anti-terror divisions. He also worked in the central apparatus, leading co-operation between the KGB, by then renamed the FSB, and the Moscow organised crime police squad. In 1997 he joined one of the FSB’s most secret departments, specialising in the pursuit of criminal organisations, and became its deputy head.

This exemplary career came to an abrupt end on November 18, 1998, when, in a press conference, he accused his FSB superiors of extortion, corruption and illegal assassinations. The accusations were detailed and seemed credible. He was suspended and in March 1999 arrested and held in isolation in the infamous KGB Lefortovo prison.

He was tried and acquitted in November 1999, but immediately rearrested. In 2000 charges were dropped after he promised to stay in Moscow. He and his family lived under intense surveillance and when they heard that further charges were being prepared, they fled. They flew to Turkey and from there to London.

Tried in absentia and sentenced to nine years in prison,Litvinenko found work in Britain as a postman, while his wife taught ballroom dancing. He continued his campaign against his former employers in interviews and books, and contributed anti-Russian material to a Chechen website. At the time of his death he was investigating the murder of the journalist Anna Politkovskaya.

He is survived by his wife Marina and his two children.

Alexander Litvinenko, former officer of the Russian secret service, was born on December 4, 1962. He died on November 23, 2006, aged 43