Yikes! My wife had been following this story, but I had not really paid much attention. But then I read this post about the significance of polonium 210 as opposed to some less remarkable poison. Some excerpts:
Polonium 210 is interesting stuff. As noted in a variety of places on the web, it is entirely artificial — it doesn't occur naturally, but has to be created by irradiating bismuth in a nuclear reactor or particle accelerator — and it has a half life of 138 days, decaying via alpha emission.
The point is, someone with access to fresh Polonium 210 (read: less than a year old, hot from the reactor) decided to use it to bump off an enemy.
And the terrorism alert status hasn't risen a notch? Pull the other one.
What this is, is a warning: "we have the capability to detonate a dirty bomb in central London any time we feel like it, so don't fuck with us". (Just take Polonium and add a little TNT.)
Who the warning is from, and who the intended recipient is, are another question entirely.