Alexander Litvinenko, who died on 23 November, 2006, aged 44, was a former Russian security officer who became an outspoken critic of the then regime in Moscow.

After dining at a London bar with two colleagues he fell ill. Three days later he was admitted to a north London hospital and after a number of routine tests it was discovered he had been poisoned.

Mr Litvinenko had become exposed to a highly toxic chemical, polonium, which ultimatelty caused his death. UK prosecutors have since brought a murder charge against former KGB agent Andrei Lugovoi.

But Russia has refused to extradite the suspect and the case has caused escalating diplomatic tensions, including the expulsion of four Russian diplomats by Britain on 16 July, 2007.

Alexander Valterovich Litvinenko, was born on August 30, 1962, in the city of Voronezh in south west Russia. He left school at 18 and joined the Soviet Army as a private. A hard working and committed individual he rose from rank to rank, culminating in his appointment as Lieutenant Colonel.

Russia was a more open and restructured country at the end of the 1980s and Mr Litvinenko joined the committee of state security, or KGB. It was the national security service in the Soviet Union and recruited many people to undertake operations to foil any threats to the country’s liberty.

As a counter intelligence officer Mr Litvinenko spent time working undercover. He was trained to deal with untoward events and in 1991 when the KGB disbanded he was responsible for tackling corruption within the newly formed FSB (the Federal Security Service)

During his employment at the FSB it is claimed that he was asked to assassinate the then secretary of the Security Council Boris Berezovsky. The assassination never took place as Mr Litvinenko refused the request, even after a violent confrontation with colleagues.

In 1998 Mr Litvinenko called a press conference where he revealed details of the assassination attempt. It was seen as an attack on the FSB and he was arrested in March 1999 by the Federal Security Service. He was imprisoned after being charged with exceeding his duties in the FSB.

Actually arrested twice, he was acquitted of all charges before leaving Moscow as an exile along with his wife Marina and their son Anatoly. Mr Litvinenko reached Britain in 2000.

He lived as an exile in London after being granted asylum and under protection from MI5, Mr Litvinenko and his family began a new life in north London.

Believing he could now speak somewhat freely about Russia, he was critical about his country’s actions in Chechnya and released a non fiction book “Blowing up Russia: Terror from Within (2002) alleging that the FSB had been behind an apartment block bombing in 1999 which killed hundreds.

Four years later Mr Litvinenko died in mysterious circumstances. After a routine meal at a sushi bar he fell ill never to recover and died in intensive care at Barnet Hospital.