Police have identified the man they believe poisoned Alexander Litvinenko. The suspected killer was captured on cameras at Heathrow as he flew into Britain to carry out the murder.

Friends of the ex-spy say that the man was a hired killer, sent by the Kremlin, who vanished hours after administering a deadly dose of radioactive polonium-210 to Litvinenko.

He arrived in London on a forged EU passport and reportedly slipped the poison into a cup of tea he made for Litvinenko in a London hotel room. Litvinenko was reportedly able to give vital details of his suspected killer in a bedside interview with detectives just days before he died on November 23 at University College Hospital.

Police have decided not to publish pictures of this man, who was seen on CCTV cameras as he flew in from Hamburg on November 1, the day that Litvinenko fell ill.

He is described as being tall and powerfully built, in his early thirties with short, cropped black hair and distinctive Central Asian features.

He reportedly travelled on the same flight as Dimitri Kovtun, a Russian businessman who is being investigated for trafficking the radioactive material used in the poison plot.

Oleg Gordievsky, a former KGB agent and friend of Litvinenko, who has worked closely with police on the investigation, said: “This man is believed to have used a Lithuanian or Slovak passport. He did not check into any hotel in London using the name or that passport, and he left the country using another EU passport.”

German police are investigating how polonium-210 was found in various locations Mr Kovtun visited in Hamburg.

According to police sources, until now it has not been revealed that Litvinenko visited a fourth-floor room at the Millennium Hotel to discuss a business deal.

He had gone to the room with Mr Kovtun and another former Russian agent, Andrei Lugovoy.

The three men were joined in the room later by the mystery figure who was introduced as “Vladislav”.

Mr Gordievsky told The Times yesterday how “Vladislav was described as someone who could help Mr Litvinenko win a lucrative contract with a Moscow-based private security company.

“Sasha (his name for Litvinenko) remembered the man making him a cup of tea.

“His belief is that the water from the kettle was only lukewarm and that the polonium-210 was added, which heated the drink through radiation so he had a hot cup of tea. The poison would have showed up in a cold drink,” he added.

The hotel room where Litvinenko thought he was poisoned remains sealed off. This room reportedly showed the heaviest concentration of polonium-210 found at a dozen locations across London.

Both Mr Lugovoy and Mr Kovtun were questioned by Scotland Yard detectives in Moscow last month. They strenuously deny playing any role in the posion plot.

Scotland Yard have asked to return to Russia so that they can continue their hunt for the suspected murderer, but have been told that they will not be allowed back until after a team of Russian investigators have completed their own inquiry in London.

The fear is that the Russian investigators will use their trip to pursue enemies of President Vladimir Putin living in London. The Kremlin has offered an amnesty for some on its wanted list in return for information against Mr Putin’s main foes given asylum in Britain. They are thought to include former executives of the fallen oil giant Yukos, whose assets have been seized by the Kremlin.

Alexei Golubovich, former director of corporate finance and strategic planning at Yukos, came back from Italy this month after striking a deal with Russian prosecutors, who had issued an international warrant for his arrest.

Mr Golubovich was held in Italy last year but fought off extradition attempts. He is now said to be co-operating actively with Russian prosecutors.

The Kremlin agreed apparently to drop fraud charges if he returned to Moscow and provided testimony against Mikhail Khodorkovsky, the founder of Yukos, and his deputy, Leonid Nevzlin.

Khodorkovsky was jailed for fraud and tax evasion in 2003 in what was widely seen as a government vendetta against the oligarch, who had been highly critical of President Putin. Mr Nevzlin fled to Israel.

Yuri Chaika, the Prosecutor-General in Moscow, has accused Mr Nevzlin of involvement in Litvinenko’s death, a charge dismissed by the former Yukos number two. Mr Nevzlin told The Times how Litvinenko flew to Israel shortly before he was poisoned to warn him about a plan by the Kremlin to claw back millions of pounds from exiled Yukos executives through a covert campaign of intimidation and murder.

At least a dozen former Yukos personnel have been given asylum in Britain. Three attempts by the authorities in Moscow to have them sent back to Russia were blocked by the English courts.

All these executives are understood to be on the list of people the Russian investigators want to question in their murder inquiry.

Mr Chaika added to the intrigue this week by announcing that Moscow had “evidence of attempts to poison several witnesses in the Yukos case with mercury”.

He also asked Scotland Yard to investigate the sudden deaths of two Russians working in London, although police here insist the men died of natural causes