I wonder why the Kremlin is so vocal on the question whether Mr Lugovoi may be extradited to London. The Russian Federation’s Constitution (adopted in 1993), Article 10, provides (unless this translation is inaccurate): “State power in the Russian Federation is exercised on the basis of the separation of the legislative, executive and judiciary branches. The bodies of legislative, executive and judiciary powers are independent.” So the extradition decision ought to be up to the courts, not the Kremlin.
As for the substantive question, Article 61(1) of the Russian Federation's Constitution provides: “The citizen of the Russian Federation may not be deported out of Russia or extradited to another state.” But it does not end there because Article 15(4) provides: "The commonly recognized principles and norms of the international law and the international treaties of the Russian Federation are a component part of its legal system. If an international treaty of the Russian Federation stipulates other rules than those stipulated by the law, the rules of the international treaty apply.” Which seems to imply that if Russia is party to an international treaty that permits extradition, the treaty overrides Article 61.
According to the BBC Mr Lugovoi himself held a press conference today and said (amid a good deal else): “I will hire serious lawyers in London in order to defend my honest name in the British law-enforcement agencies. If the British authorities refuse to conduct a fair trial, I will be prepared to appeal to the international court in The Hague." By "British authorities" does he mean the judiciary? And what trial does he have in mind? Does he think that he might be extradited? I take it that he does not intend to come to London voluntarily to be tried on the poisoning charge. Perhaps he envisages a different kind of trial - bringing a claim himself in the civil courts for defamation? I wonder who the defendant(s) would be, and how Mr Lugovoi would give evidence: not by personally attending court in London, presumably. We must wait to find out.
To bring such a claim would imply, interestingly, a degree of trust in the impartiality of the judiciary of England and Wales. He does, it seems, have time for lawyers, at least the "serious" variety, which is a nice bit of good press for them, for a change.