The death of Mr Litvinenko - a bitter foe of Russia's president, Vladimir Putin - bears all the hallmarks of a political murder.

Getting your hands on enough radioactive polonium - the apparent murder weapon - to poison someone requires access to a nuclear reactor or a particle accelerator, according to Professor Dudley Goodhead, of the Medical Research Council & Genome Stability Unit. That narrows the field of potential suspects considerably.

Despite official assurances that they have turned over a new leaf, it is well-documented that Russian spies have made a habit of using sophisticated poisons to eliminate their enemies. Indeed, even if common criminals could somehow have obtained some polonium, why would they bother using such esoteric means to kill Mr Litvinenko when they could more easily have had him stabbed or shot?

In short, although there is no concrete proof as yet, it is certainly reasonable to believe that the Kremlin had a hand in the murder of Mr Litvinenko, who himself pointed the finger at Putin before he died. The Russian authorities certainly had both motive and means, as well as reasons to try to cover their tracks. Pointedly, the SVR, the KGB's new guise, went to the lengths of denying responsibility - not because killing Mr Livninenko was inconceivable or wrong, but because it was said not to be worth the damage to relations with Britain.

How should the West react?

John Thornhill writes in the FT that:

the west should remain open to the Russian people. Western European countries should, if anything, ease visa restrictions for Russian visitors and encourage young Russians to study abroad. EU countries should encourage mutually beneficial business, financial and cultural ties wherever possible.

However, Europe must remain united in the face of any intimidation and not allow the Kremlin to play one country off against another. EU countries should reduce their dependence on Russian energy supplies if Moscow is going to regard them as a political tool. They should continue to denounce human rights abuses in Chechnya – and elsewhere – as being incompatible with the standards of the international organisations to which Russia belongs. And Britain should be firm in prosecuting whoever is responsible for Alexander Litvinenko’s death, no matter where the investigation leads.

Quite right too.