Dr Julian Lewis: Has the Foreign Secretary [David Miliband] received any expert advice on the likelihood of a private citizen having been able to obtain a lethal quantity of polonium-210 from anything other than a Government-controlled nuclear agency, and has he suggested to the Russian Government that if they go down the old Cold War route of tit-for-tat expulsions he has something else up his sleeve? I do not, of course, expect him to specify what.