Two more people have tested positive for the radioactive substance which killed a former Russian spy.
Mr Litvinenko was a known critic of Russia's security services
It brings the total number affected by polonium-210 and facing possible health risks to 15.
In November, ex-KGB agent Alexander Litvinenko died after being poisoned by the substance in London.
The Health Protection Agency (HPA) say those also contaminated are people who visited the same areas as him on the day he was exposed.
Mr Litvinenko, 43, visited a number of sites in the capital on 1 November, including several hotels, an Italian restaurant in Mayfair and the Itsu sushi bar in Piccadilly.
He also drank at The Pine Bar at the Millennium Hotel in Mayfair and according to the HPA one of the most recent victims also visited it that day.
The HPA, which carries out the tests for radiation, says the second victim is a member of staff from the Sheraton Hotel Park Lane.
Neither are expected to fall ill in the short term, but both do have a slightly greater risk of developing cancer in the long term, it said.
A spokeswoman for the HPA said: "The average person in the UK has a 23% chance of developing cancer and for these people that risk is increased by around 0.05%."
Father-of-two Mr Litvinenko died at London's University College Hospital on 23 November and Scotland Yard are currently investigating his murder.
As well as the 15 facing possible health effects, another 119 people have been found with polonium-210 in their bodies, but at levels too low to cause concern.