Scotland Yard said that counter-terrorism officers would be taking their investigation into the death of ex-KGB spy Alexander Litvinenko to Moscow within the next few days.
The revelation came as one of the most senior former figures in the intelligence world appeared to point the finger of blame directly at the Russian state. As the theories continued to abound as to why and how Mr Litvinenko came to be poisoned with the deadly radioactive substance polonium-210, Metropolitan Police sources suggested nine officers would be travelling to Moscow but would not reveal who they want to interview.
Among those likely to be considered is the former Russian intelligence officer Mikhail Trepashkin, who is currently in jail for revealing secret information. In letters smuggled out of Russia last week he offered himself as a witness and claimed that a secret hit squad had been set up to target Mr Litvinenko as well as others.
Meanwhile, Dame Pauline Neville-Jones, the former chairman of the Joint Intelligence Committee, told BBC 1's Sunday AM programme: "The question you have to ask yourself, I suppose, is, 'Who has the motive and who has the capability?' There's quite a lot of people potentially, I think, who have the motive. The capability, I think, ties it much more to some organ of the Russian state. You can't buy polonium in the chemists, so it has to come from some source that's able to produce it."
Last week the Kremlin denied claims that linked President Vladimir Putin to the poisoning, insisting it was disappointed with "hysteria" in the British media.
Ten days after Mr Litvinenko's death, the investigation continued to widen as the Home Secretary, John Reid, said: "The police will follow wherever this investigation leads inside or outside of Britain. That will continue over the next few days." Mario Scaramella, the Italian academic who met Mr Litvinenko at Itsu sushi restaurant on 1 November and later tested positive for polonium-210, was said to be well and continued to show no symptoms of poisoning, University College Hospital in London said. Doctors were due to carry out fresh tests on Mr Scaramella yesterday as his lawyer, Sergio Rastrelli, conceded his client was "clearly worried" even though his dosage of polonium was far less than that which apparently killed Mr Litvinenko.
A variety of theories continued to emerge, including claims that Mr Litvinenko planned to make money blackmailing senior Russian spies and business figures. The London-based Russian academic, Julia Svetlichnaja, told The Observer: "He told me shamelessly of his blackmailing plans aimed at Russian oligarchs. "'They have got enough, why not to share? I will do it officially', he said."
It was also claimed that the fierce Kremlin critic had obtained a dossier containing damaging information about the Russian government and the break-up of the oil giant Yukos.
While police sources admitted officers had been to Washington, Scotland Yard declined to comment on reports that British detectives have interviewed the former KGB officer, Yuri Shvets, in the US over a dossier he may have compiled on issues relating to Yukos.
Leonid Nevzlin, a former shareholder of the oil giant who now lives in Israel, has claimed that a document on Yukos that Mr Litvinenko gave him may have provided a motive for someone to kill him.
Mr Litvinenko's wife Marina was found to have a very low level of polomium and her son Anatole, 12, has tested negative for the substance.
The NHS Direct phone line has now received 3,025 calls from worried members of the public. It has singled out 179 people for further investigation and referred 27 to a specialist clinic for radiological exposure tests.Reuse content