With the news that the body of murdered ex-spy Alexander Litvinenko will, after all, get a postmortem – it was initially thought that the amount of radioactive material in his body would make it impossible – the case of the poisoned sushi is getting more interesting by the minute.

Should they be able to collect enough of the polonium 210 that killed Litvinenko – administered either in a drink at the Millennium Bar or via sushi from the fashionable Itsu restaurant – it may be possible to tell where it came from via spectrographic analysis, its atomic fingerprint.

This would mean that if there has been official Russian government involvement, it will be a lot more likely to come out.  Litvinenko’s plight looked like a James Bond movie last week, and I wasn’t the only who rocked up to Itsu to see and eat at the place where the ex-spy got poisoned.

I couldn’t get a seat – which looks lucky now. The whole place is being decontaminated and between three and 18 people from across London – reports vary – are in a special clinic having tested positive for possible contamination.

Undetectable if carried in a sealed container, polonium 210 is one of the most poisonous substances on earth if consumed or breathed in. Litvinenko’s house had been firebombed a fortnight earlier, but why go to such elaborate lengths to kill a former FSB (the new KGB) man turned investigative journalist? How did they get it into the restaurant or the bar and into his food or drink?

One theory is that it’s an unauthorised job by a faction within the FSB, with the means of assassination acting as a calling card to both prospective renegade agents, and to former KGB head Putin himself, to let him know who’s boss. The involvement of a judo-master FSB operative named Igor has been seriously suggested.

The other is that Litvinenko knew so much about Putin’s theft of the Yukos oil group – which had been stolen by its owners anyway – that he just had to be killed, even at the price of this sort of publicity.

Ironic really, that the first genuine radioactive threat to London – which must be high on the target list for a dirty bomb – most likely comes from our ally in the “war on terror”. No coincidence that one of Litvinenko’s contentions was that the FSB had been responsible for the bombing of two Moscow apartment blocks in the 1990s – at the time attributed to Chechen separatists, and a trigger for the escalation of the utterly ruthless destruction of Chechnya in the past seven years. Turn a blind eye to state thuggery and it eventually comes back on you.

Just as the dirty bomb that eventually hits London or New York will almost certainly come from technology supplied by AQ Khan, the bombmeister of our ally Pakistan, so too in this case, it is our friends who present the greatest threat. Never mind. If it is eventually traced back to Putin, he can simply say that he didn’t read the memos.