Mario Scaramella, the Italian academic who met the ex-Russian spy Alexander Litvinenko on the day he fell ill, has been discharged from hospital.
Mario Scaramella met Mr Litvinenko the day he fell ill
Mr Scaramella was under observation after testing positive for the highly toxic isotope polonium-210, which has been linked to Mr Litvinenko's death.
Earlier doctors had said Mr Scaramella had not shown any signs of illness.
Meanwhile, a contact of the ex-spy is to meet British detectives in Moscow, the BBC has learned.
Mr Scaramella had met Mr Litvinenko on 1 November at a sushi bar in central London.
A spokesman for University College Hospital in London said Mr Scaramella was not showing any symptoms of radiation poisoning.
The Health Protection Agency also confirmed that staff at the restaurant where the pair met had all tested negative for radiation.
Meanwhile, former KGB bodyguard Andrei Lugovoi is expected to talk to Scotland Yard investigators in the Russian capital, his business associate Vyacheslav Sokolenko said.
Andrei Lugovoi has denied any involvement in the poisoning
Mr Sokolenko confirmed he was in London with Mr Lugovoi on 1 November but said 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.
Nine Metropolitan police officers are currently in Moscow but have had restrictions placed on their investigations into Mr Litvinenko's death by the authorities.
Russia's chief prosecutor, Yuri Chaika, said his own officers would be conducting any witness interviews, British officers could not arrest Russian citizens and suspects would not be extradited to Britain.
Scotland Yard's anti-terrorism unit has not confirmed who officers will be meeting.
Mr Lugovoi 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.
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 1 November.
Earlier, Mr Scaramella said he had received a "general alert" about the former spy's security.
In an interview from his hospital bed he told CNN he had travelled to London for a conference, but had changed his plans to discuss the threat with Mr Litvinenko .
He said had received e-mails claiming that both he and Mr Litvinenko were "under the special attention of hostile people", but neither man believed the threats were real.
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."
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".