Either the Russians thought of an extremely novel use for Polonium 210 (to murder), were conducting a test (such as the ease they can smuggle it past Western detection), proving someone's bona feds, or they were smuggling it to rogue elements (inside or outside England) and/or rogue regimes. I think these are all viable possibilities at this point, especially after reading the following:
The agency's chief executive, Pat Troop, said the high level of polonium-210 indicated Litvinenko "would either have to have eaten it, inhaled it or taken it in through a wound."
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Chris Lloyd, a British radiation protection adviser, said it would be relatively easy to smuggle polonium into a country, because its alpha radiation would not set off radiation detectors.
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Professor Dudley Goodhead, a radiation expert at the Medical Research Council, said that "to poison someone, much larger amounts are required and this would have to be manmade, perhaps from a particle accelerator or a nuclear reactor."
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The Health Protection Agency said the use of polonium as a deliberate poisoning would be "an unprecedented event." Several experts also said they were unaware of any other known poisonings from the element.
"I've been in radiation sciences for 30-odd years and I'm not aware of any such incident," said Roger Cox, director of the agency's center for radiation, chemicals and environmental hazards.
http://wtop.com/?nid=383&sid=985629&sidelines=1Also...
What is the risk to other people from the dose Mr Litvinenko received?
It cannot pass through the skin, and must be ingested or inhaled (or delivered through a wound as per above--GGG) into the body to cause damage.
And because the radiation has a very short range, it only harms nearby tissue, so those who came into contact with him are at very little risk.
William Gelletly, professor of physics at the University of Surrey, said: "Polonium-210 is very unlikely to have contaminated any staff who treated Mr Litvinenko or anyone who came in contact with him since they would have had to ingest or breathe in the contaminated fluids from his body."
http://news.bbc.co.uk/2/hi/health/6181688.stm