Probably

"Litvinenko - What Really Happened?"  A much more plausible alternative theory.  Obvious problems with the Putin-polonium theory:

1. why would you use a complex James Bond-ish assassination scenario when there are so many easier methods, like, say, a gun?;
2. why would you use a method that is traceable back to the source of the weapon?;
3. why would Putin care about Litvinenko at all?;
4. why would you use a method that is dangerous for the assassins themselves?

There is no evidence for the smuggling theory, but it is much more plausible. I can see an accident happening, resulting in the certain death of Litvinenko, with he and Berezovsky then concocting a story to frame their mutual enemy Putin, with some money going from Berezovsky to Litvinenko's family. That story actually makes sense.

What kind of public inquiry comes up with a conclusion that something 'probably' happened.  I can see saying Putin did it, or saying there is no way to know what happened, but saying Putin 'probably' did it?  Following Hutton and Chilcott, British public inquiries have become a laughingstock.

"Britain had more motivation to kill Aleksandr Litvinenko than Russia, brother claims"

Similar nonsense, which is everywhere these days:  "Kerry Pressed for MH-17 Evidence"