Hundreds of people have called the NHS Direct hotline following the death of Russian ex-spy Alexander Litvinenko.
The post-mortem examination on Mr Litvinenko has been delayed
The Health Protection Agency has urged anyone else who visited the same London hotel or sushi bar on 1 November, when he met his contacts, to get in touch.
Mr Litvinenko's death has been linked to the presence of a "major dose" of radioactive polonium-210 in his body.
Radioactive traces have been found at the Itsu restaurant in Piccadilly and the Millennium Hotel's Pine Bar.
But the HPA says the risk of contamination to other people is low.
A spokeswoman for the Department of Health (DoH) said up to 300 people had called NHS Direct after the HPA asked people to make contact.
Home Secretary John Reid said the government was doing all it could to keep people informed about the situation.
He told BBC Radio Clyde: "We're trying to put as much information into the public domain as we can."
Mr Reid said this included alerting people about the health hazard and offering advice through various means, including NHS Direct.
He added that police were now treating Mr Litvinenko's death as suspicious, rather than "unexplained".
"As at this stage, they're saying to me that they now regard the death as suspicious. That wasn't the case yesterday [Saturday], for instance," Mr Reid said.
In other developments:
- Police forensic searches at Itsu are now complete and the premises are being decontaminated
- Officers have also been searching a bedroom at the Millennium Hotel
- A post-mortem examination on Mr Litvinenko has been delayed over health implications for those present at the examination
Friends have said Mr Litvinenko was poisoned because of his criticism of Russia.
In a statement dictated before he died at University College Hospital on Thursday, the 43-year-old accused Russian President Vladimir Putin of involvement in his death. He was known to be a fierce critic of him.
Mr Putin's spokesman Dmitry Peskov reiterated the Kremlin's earlier dismissal of allegations of involvement in the poisoning as "sheer nonsense".
The president himself has said Mr Litvinenko's death was a tragedy, but he saw no "definitive proof" it was a "violent death".
Russian newspapers - many of which are controlled by the Kremlin - have also reacted angrily to implications that Moscow was involved in Mr Litvinenko's death.
Andrei Nekrasov, who was close to Mr Litvinenko, said his friend had been a "strong man" who was left so debilitated by the rapid deterioration of his health that he was "reduced" to "screaming from pain".
Forensic tests were also carried out at the dead man's home
Speaking on BBC 1's Sunday AM show, Mr Nekrasov also said that he did not believe Mr Putin was "directly" responsible, although he thought "rogue elements" connected to the Russian leader were.
He said: "I think that Putin's orders on this are unlikely.
"Those rogue people are, in my opinion, a direct responsibility of Mr Putin. They are the result of the ideology of falsely understood nationalism which is now being injected into the Russian people."
Meanwhile, the Conservatives are to call for a Commons statement on Mr Litvinenko's death.
Shadow home secretary, David Davis, intends to raise the matter when MPs return to Westminster on Monday.
Mr Davis is expected to question ministers about the safety of Russian dissidents in the UK and to ask how polonium-210 was brought to the UK.
He also said it was important that there was full co-operation from anyone who may be able to help the police - including the Russian authorities.
"It is essential that other dissidents living in Britain are reassured about their safety and there are also questions about how polonium-210 came to be used in Britain," he said.
Mr Reid has rejected calls for a Commons statement, saying he would keep the situation under review.
Liberal Democrat leader Sir Menzies Campbell said if the Kremlin was found to be behind Mr Litvinenko's death then Britain should "consider very carefully" its future relationship with Russia.
UK civil contingencies committee, Cobra, has met to discuss the case.