Home secretary John Reid has urged the public to keep calm after traces of the radioactive substance polonium 210 were found at London locations associated with the death of poisoned Russian spy Alexander Litvinenko. Traces of the radioactive substance were found at a London sushi restaurant where Alexander had a meeting, his London home and also a London hotel. There were also unconfirmed reports that the substance had been found at two other London locations. Mr Reid also confirmed that a "significant quantity" of polonium 210 had been found in Mr Litvinenko’s urine following extensive tests by forensic toxicologists. I’ve been following the story of Alexander Litvinenko. According to news reports polonium 210 is an extremely rare substance that needs to be manufactured using a nuclear reactor. With security so tight at Britain’s airports and seaports following terrorist threats, I would be surprised if anybody could get through with a substance of this nature. There are many theories as to who caused Alexander Litvinenko’s death. Sadly we will probably never know.