A contact of ex-Russian spy Alexander Litvinenko is to meet British detectives, the BBC has learned.
Andrei Lugovoi has denied any involvement in the poisoning
Former KGB bodyguard Andrei Lugovoi will talk with Scotland Yard investigators, his business associate Vyacheslav Sokolenko said.
Mr Sokolenko confirmed he was in London with Mr Lugovoi on 1 November but that he did not meet or know Mr Litvinenko.
He said the meeting would be at the clinic where he says Mr Lugovoi is undergoing medical checks.
Russian officials are expected to conduct the interviewing of Mr Lugovoi on Wednesday but British detectives will be in attendance.
He had previously given a statement to the British Embassy in Moscow after seeing his name appear in the media in association with investigations.
"If they show me a list of people that they want to meet and if there are names missing on that list, names that I believe would be interesting to propose to them, then I certainly will," Mr Lugovoi previously told NTV television.
Mr Lugovoi and another Russian businessman are reported to have met Mr Litvinenko on 1 November.
Russia will not extradite suspects in the Litvinenko case
Vyacheslav Sokolenko has denied ever meeting Mr Litvinenko and told the BBC he was in London, but only to watch the football.
He says Mr Lugovoi and Dmitry Kovtun met Mr Litvinenko, but he was not present, adding he never knew the ex-spy.
Nine British police officers are currently in Moscow but have had restrictions placed on their investigations into Mr Litvinenko's death by the authorities.
Scotland Yard's anti-terrorism unit has not confirmed who officers will be meeting.
Russia's Chief Prosecutor, Yuri Chaika, has said his own prosecutors would be conducting any witness interviews.
He said it was "impossible" for British officers to arrest Russian citizens and confirmed that suspects in the poisoning will not be extradited to Britain.
British police launched their investigation after Mr Litvinenko, 43, died in a London hospital on 23 November.
Tests have been carried out at a number of venues the ex-spy visited in London on November 1 - the day he fell ill.
A hotel and an office are the latest central London locations to be tested for signs of the deadly toxin found in the ex-KGB agent's body.
A room at the British Embassy in Moscow is also being tested as a precaution.
Meanwhile, an Italian contact of Mr Litvinenko said he had received a "general alert" about the former spy's security.
Mario Scaramella, who has also tested positive for polonium-210, the radioactive substance that apparently killed the former spy, told CNN he had travelled to London for a conference, but had changed his plans to discuss the threat with Mr Litvinenko .
The two men met on 1 November at the Itsu sushi restaurant in Piccadilly, central London.
In an interview from his hospital bed, he said: "I received in the days before a general alert about him in terms of security. Once here I received more details about this risk, this danger."
Mr Scaramella, who is being treated at London's University College Hospital, said he had received emails claiming that both he and Mr Litvinenko were "under the special attention of hostile people".
Neither man believed the threats were real, he said.
When asked what kind of people would be targeting him, he said: "People linked with some clandestine organisations, not directly under control of Russian establishment but from Russia."
Mr Scaramella said he did not believe he had been deliberately poisoned because he was "perfectly well".
He only had about a 20th of the dose found in Mr Litvinenko's system, he said.
The Health Protection Agency has confirmed none of the Itsu sushi restaurant staff who provided urine samples as a result of the radiation scare have tested positive for polonium-210.
Friends believe Mr Litvinenko was poisoned because of his criticisms of the Russian government, but the Kremlin has dismissed suggestions it was involved in any way as "sheer nonsense".