Ros Taylor details key events before and after the death of former Russian spy Alexander Litvinenko

October 7 2006: Journalist Anna Politkovskaya, a prominent critic of the Russian government and the war in Chechnya, is found dead in her apartment building in Moscow with two gunshot wounds. Colleagues say she had been threatened because of her views. In Britain, former Russian spy Alexander Litvinenko, another outspoken critic of the Kremlin, begins to investigate the murder.

November 1 2006: Mr Litvinenko meets a number of Russian men at the Pine Bar of the Millennium Hotel in London, including the businessmen Andrei Lugovoi, a former KGB agent, and Dmitry Kovtun. Later, he meets the Italian academic Mario Scaramella at a sushi bar in Piccadilly. Several hours later, Mr Litvinenko complains of feeling sick and is admitted to hospital.

November 11 2006: Mr Litvinenko tells the BBC's Russian Service he has been poisoned. Commenting on the meeting with Mr Scaramella at the sushi bar, he says: "He passed me some papers, where the person was named, who apparently might be connected to the murder of Anna Politkovskaya."

November 19 2006: Reports emerge in the British press that Mr Litvinenko, whose condition has deteriorated, has been poisoned with thallium. Doctors give him a 50/50 chance of surviving the next few weeks.

November 20 2006: Dramatic pictures of Mr Litvinenko in his hospital bed show his hair has fallen out. Scotland Yard says detectives are treating the case as a suspected "deliberate poisoning" but are awaiting the results of toxicology tests. A Kremlin spokesman dismisses allegations that the Russian government was involved in the poisoning as "sheer nonsense".

November 21 2006: A toxicologist suggests radioactive thallium may have poisoned Mr Litvinenko. Mr Scaramella claims Mr Litvinenko saw documents naming him as a target during their meeting on November 1.

November 22 2006: Mr Litvinenko's condition continues to deteriorate. Russia's foreign intelligence service denies involvement in the poisoning, suggesting he was small fry.

November 23 2006: Mr Litvinenko dies after suffering a heart attack.

November 24 2006: A statement dictated by Mr Litvinenko on November 21 is released. He tells the "person responsible" for his poisoning: "You have shown yourself to be as barbaric and ruthless as your most hostile critics have claimed." The Health Protection Agency says tests have established that Mr Litvinenko had a "significant quantity" of the radioactive isotope polonium-210 in his urine. It confirms that traces of radiation have been found at the sushi bar and the Millennium Hotel.

November 27 2006: John Reid, the home secretary, says the Russian authorities have been asked to provide "all necessary co-operation" with the investigation. Scotland Yard says traces of polonium-210 have been found at offices in Mayfair. One was visited by Mr Litvinenko and another is the office of exiled billionaire Boris Berezovsky, a friend of Mr Litvinenko.

November 29 2006: British Airways says "low levels of radioactive traces" have been found on two of its aircraft. Experts are preparing to examine a third aircraft in Moscow, it added.

November 30 2006: The coroner at the inquest into Mr Litvinenko's death confirms it appears he had been exposed to, or administered, polonium-210. The inquest is adjourned. Aides of the gravely ill former Russian prime minister Yegor Gaidar claim doctors treating him in Dublin believe he has been poisoned.

December 1 2006: Mr Scaramella tests positive for a significant quantity of polonium-210. Alex Goldfarb, a friend of Mr Litvinenko, reveals that two smuggled letters from a jailed Russian ex-intelligence officer allege that the FSB, the successor to the KGB, had set up a special group to target Mr Litvinenko and other dissidents.

December 4 2006: A team of Scotland Yard detectives flies to Moscow to interview a number of potential witnesses, including the Russians who met Mr Litvinenko on the day he fell ill. Russia's foreign minister, Sergey Lavrov, warns that persistent suggestions of Russian involvement in his death could harm diplomatic relations between London and Moscow.

December 5 2006: Minute quantities of radiation are found at Arsenal's Emirates stadium. The radiation is found at the north London stadium at "barely detectable levels". The limitations of the inquiry become clear when Russia's chief prosecutor, Yuri Chaika, says no suspects will be extradited to the UK and all Russian citizens suspected of involvement would be tried in Russia.

December 6 2006: Scotland Yard announces it is now treating the death of Mr Litvinenko as murder. Mr Scaramella is discharged from hospital after doctors conclude he does not have radiation poisoning.

December 7 2006: Mr Litvinenko's funeral takes place at Highgate Cemetery. Seven members of staff who were working at the Pine Bar on the day Mr Litvinenko was there test positive for polonium-210.

December 11 2006: A Scotland Yard detective investigating Mr Litvinenko's death travels to Hamburg. He is briefed on the German investigation, which focuses on houses and property linked to Russian businessman Dmitry Kovtun. German police say Mr Kovtun was being investigated on suspicion of illegal handling of radioactive material, but they do not link him to Mr Litvinenko's poisoning. Dmitri Peskov, a spokesman for the Russian president Vladimir Putin, insists it is "unthinkable" that the Russian government could be behind any killing.

December 19 2006: Britain seeks help from France to question a Russian living in the French Alps who has been linked to the case. Yevgeny Limarev is expected to be questioned by a French magistrate, with British officials in attendance. Mr Limarev has been described as a KGB defector, although he disputes that, saying he works as a consultant specialising in Russian politics and security issues. Mr Limarev also disputes reports that he told Mr Scaramella that Russian security veterans were plotting to kill Mr Litvinenko and other Kremlin critics.

December 24 2006: Italian police investigating claims of arms trafficking and the leaking of state secrets arrest Mr Scaramella in Naples. The arrest is not part of the investigation into Mr Litvinenko's murder.

January 5 2007: An Italian restaurant in Mayfair is the latest location to be contaminated with polonium-210. It is believed to be among the locations visited by Andrei Lugovoi and the other men who met Mr Litvinenko at the Millennium Hotel on the day he fell ill.

January 27 2007: Mr Lugovoi criticises a Guardian report naming him as a suspect in the murder and denies any role in the killing. January 31 2007: Scotland Yard says it has sent a file on the case to prosecutors.

February 6 2007: A London press conference to launch a new book co-written by Mr Litvinenko is cancelled at the last minute "for security reasons". Co-author Yuri Felshtinsky says security experts believed he was at risk.

March 19 2007: Business tycoon Boris Berezovsky points the finger of blame at Mr Putin: "I don't think that Putin gave the order to kill him [Litvinenko] by poison polonium, but I'm sure that Putin is behind it and [there is] no chance without Putin to obtain polonium and organise this plot."

April 3 2007: Mr Litvinenko's widow Marina launches the Litvinenko Justice Foundation to campaign for his killers to be brought to justice.

May 22 2007: The Crown Prosecution Service says there is enough evidence to charge Mr Lugovoi with murder and it will apply for his early extradition from Russia.

May 28 2007: The UK's ambassador to Moscow makes a formal extradition request for Mr Lugovoi. Russian officials say Russian law does not permit such an extradition but there are signs the Kremlin would countenance a "swap" for Mr Berezovsky, who it wants extradited from the UK.

May 31 2007: Mr Lugovoi tells a press conference in Moscow that the UK's intelligence services were involved in the death of Mr Litvinenko, who he claimed was working for MI6. Mr Lugovoi also claimed that British intelligence had tried to recruit him during previous years when he was on business trips, seeking "compromising information" on Mr Putin.

June 1 2007: Russia's foreign minister, Sergei Lavrov, accuses Britain of using the Litvinenko case to wage a political campaign and says the affair has damaged relations between London and Moscow. "Instead of a professional inquiry, we are seeing an attempt to turn the criminal case into some sort of political campaign. We are against that," he says.

June 3 2007: Mr Putin reiterates his foreign minister's comments, accusing Britain of "politicising" Mr Litvinenko's murder.

June 8 2007: Then prime minister Tony Blair meets Mr Putin for talks which include the Litvinenko case. June 11 2007: Mr Blair tells Parliament: "I can't say that we've made great progress on the Litvinenko case. We will continue to do all we can to press the Russians on this issue."

June 14 2007: Russia demands that the cultural organisation, the British Council, moves out of one of its offices in the Russian city of Yekaterinburg. The move is the latest in a campaign of harassment against the council and is believed to be partially linked to poor relations between the two countries over the Litvinenko affair.

June 15 2007: Russia announces its own investigation into the case. In a one-sentence statement the federal security service in Moscow says it has started an espionage inquiry into claims made by Andrei Lugovoi.

July 5 2007: The Crown Prosecution Service announces Mr Litvinenko's friend, exiled Russian billionaire, Boris Berezovsky, will not face charges in the UK for talking to the Guardian about plotting a "revolution" in his homeland. Kremlin officials call it a "disturbing moment" in anglo-Russian relations. He is to be tried in Russia, in his absence, accused of embezzlement and money laundering.

July 9 2007: Russian officials formally tell the UK they will not extradite Mr Lugovoi.

July 10 2007: Downing Street describes the decision not to extradite Mr Lugovoi as "extremely disappointing".

July 16 2007: David Miliband announces the expulsion of four diplomats from the Russian embassy in London because of the failure to extradite Mr Lugovoi.

July 17 2007: Russia's deputy foreign minister, Alexander Grushko, promises an "adequate and appropriate" response to the expulsions, but does not signal when it will happen. He says the counter-measures will take into account the interests of "ordinary British citizens and businessmen".