Nearly a fifth of the people tested for the radioactive substance which killed former Russian spy Alexander Litvinenko have tested positive for contamination.
Alexander Litvinenko died in London on 23 November 2006
The Health Protection Agency (HPA) found that 120 of the 596 people tested showed traces of radiation. But just 13 were deemed to have a health risk.
The HPA said the levels found were unlikely to cause a short-term illness and the long-term risk was very small.
Mr Litvinenko, 43, died in University College Hospital, London, in November.
The HPA's chief executive, Professor Pat Troop, said: "There are just over 100 people who had evidence that they were in contact - most probably in contact - with this radiation polonium-210."
The agency has identified 450 people who may have been affected worldwide by radiation.
It is working with 48 different countries as part of this process.
Prof Troop said tests were still being carried out on a number of foreign nationals who may have been contaminated.
Mr Litvinenko visited a number of central London venues on the day that he fell ill.
The Millennium Hotel in Mayfair, the Itsu sushi bar in Piccadilly and an Italian restaurant, also in Mayfair, were among the addresses.
Prof Troop said the amount of contamination in the former spy's body was "many thousands of times greater" than anyone else who had tested positive for polonium-210.