A company in the US claims to supply polonium-210 to anyone for just $69 plus postage and packing. A three-pack set of “alpha, beta, gamma” radioactive isotopes also includes polonium-210.

United Nuclear, based in Albuquerque, New Mexico, tells purchasers: “If you’re looking for clean, accurate, certified radiation sources, here they are. . . All isotopes are produced fresh in a nuclear reactor and shipped directly to you.”

The company says that it has supplied radioactive materials to “the science hobbyist”, businesses, government bodies and teachers since 1998. “We specialise in small orders.” United Nuclear assures customers that they run no risk of being tipped off to the US Department for Homeland Security.

“Chemical suppliers routinely forward customers’ names, along with their purchases, to government officials/Homeland Security officials etc. We do not — and never will. We respect your privacy and will fight for it,” the company’s website states.

The Los Alamos National Laboratory in New Mexico describes polonium-210 as 250 billion times more toxic than hydrogen cyanide. The apparent availability of polonium-210 intensifies the problems facing Scotland Yard detectives in establishing the source of the poison that killed Mr Litvinenko in London last week.

Many commentators have asserted that the material could only have come from a state-controlled nuclear facility, leading critics of President Putin to point the finger at Russia’s secret service.

Sergei Kiriyenko, head of Russia’s atomic energy agency, has revealed that it sells 8g of polonium-210 each month to American companies for “scientific purposes”.

United Nuclear says it accepts orders only through its online service and that materials can be sent only to addresses in the US. But it is not difficult to arrange for a delivery in the US to be forwarded to another country.

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