John Reid, the interior minister, told parliament on Monday that traces of polonium 210 had been found in two hospitals where Litvinenko had spent his dying days, a sushi bar and a hotel he visited on November 1, as well as "certain" other places in London.
Health officials have offered tests to members of the public who may have visited the contaminated locations.
Minister criticises Russia
Litvinenko, 43, a former KGB agent and fierce critic of Russian President Vladimir Putin, died on Thursday after being poisoned by the radioactive element polonium-210
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Britain also announced it will open a formal inquest on Thursday into the death of Litvinenko, local government officials said.
Opening an inquiry is a legal formality, and such inquests are almost always adjourned immediately, sometimes for months.
Amid increasing speculation that the former spy was assassinated by Russian intelligence services, British officials have criticised the lack of freedom and human rights in Russia.
Peter Hain, the Northern Ireland minister, said that although Vladimir Putin, Russia's president, had shown promise, it has been "clouded by what's happened since, and including some extremely murky murders" including that of the prominent Russian journalist Anna Politkovskaya in October.
Politkovskaya was a vocal critic of the Kremlin and Litvinenko had been allegedly investigating her death in October.
Hain told the BBC there had been "huge attacks on individual liberty" in Russia and said it was important that Putin "retakes the democratic road".
The UK government also convened a meeting on Monday of senior ministers, officials and experts to assess the potential threat from radioactivity to Londoners.