A former Russian spy is fighting for his life in a London hospital after being poisoned with the lethal substance thallium. Pictures published yesterday showed Alexander Litvinenko, who was in the prime of life only two weeks ago, a shadow of his former self. Yesterday he was returned to intensive care after his condition worsened.

There is no reason to beat about the bush. This attempted murder, for that is surely what it is, bears all the hallmarks of the Russian security services, the FSB. Thallium, without taste and fatal in even tiny quantities, is the secret services' drug of choice. Its last known use was against the Ukrainian opposition politician, Viktor Yushchenko, when he was standing for the presidency. In the case of Mr Litvinenko, the Kremlin had plenty of reasons for wanting the troublesome former FSB lieutenant colonel out of the way for good.

Mr Litvinenko was indicted three times for treason in Russia in the late Nineties. He was twice cleared, and defected to Britain where he was granted political asylum before the last case against him was heard in absentia. He used what he presumably felt was the safety of Britain to expose the black arts of the FSB. He wrote a book, which was sponsored by the former oligarch who is probably the Kremlin's chief bête noir in London, Boris Berezovsky. And last month he publicly held President Putin responsible for the murder of the investigative journalist Anna Politkovskaya.

Neither Mr Litvinenko's high public profile, nor the associates he chose in exile, were calculated to endear him either to the Russian authorities or to his former colleagues. He was clearly a man who lived dangerously, eschewing the judicious silence that might have kept him out of harm's way. Like Ms Politkovskaya, he made no secret of his hatred of Mr Putin and held it a point of principle to speak his mind. Despite the Kremlin's characteristically tardy denial yesterday, the evidence points in that direction. That this might be a freelance operation by aggrieved former colleagues is not necessarily more reassuring. What would this say about the reach of Mr Putin's authority in Russia?

This case has two other profoundly disturbing aspects. The first is that Russia's leaders - or the secret services acting on their behalf - appear to be returning to venal Soviet ways. Those who voice dissent risk being silenced; another critic of the Chechen war was sent to prison yesterday. Those who do not heed initial warnings may reasonably fear for their lives. This is very far from being the free and democratic Russia that we hoped would rise from the wreckage of communism.

The second is the evidence that it supplies of increasingly brazen FSB activity abroad, targeted specifically on the emigrant community. Accounts differ about precisely how or where Mr Litvinenko was poisoned, but it appears that it was at a meeting, probably with one or more former colleagues, in the very centre of London. Our capital has become a centre for Russians living, working or just visiting abroad. Every strand of Russian politics and society is represented here. It is perhaps not surprising that in this relatively relaxed and cosmopolitan atmosphere, foreign security services feel free to go about their business and murderous plots may be hatched.

Until now, with the exception of the high-profile super-rich, such as Roman Abramovich, the Russians have not drawn attention to themselves. The Litvinenko poisoning will bring unwelcome scrutiny. But it should also alert our police and security services to lurking danger. If those granted refuge here obey our laws, we have an obligation to extend to them the full protection of the law. Alexander Litvinenko deserved to have his fears taken more seriously than they were.