On Thursday evening events surrounding the death of Alexander Litvinenko, the former Russian spy poisoned in London, took another surreal turn.

The Russian news agency Interfax reported that Dmitri Kovtun, a former spy who had come to London and met Litvinenko on the day he was poisoned, had fallen into a coma. Kovtun had apparently suffered radiation poisoning from polonium-210 and was desperately ill.

It seemed that a key witness and possible suspect had been a victim of the plot as well as the exiled dissident Litvinenko.

The report of Kovtun’s coma came as a shock to Mark Franchetti, The Sunday Times’s Moscow correspondent, since only two hours earlier he had been speaking to Kovtun, who had sounded perfectly healthy. He hurriedly rang him.

At first, he got no reply. But eventually he reached Kovtun, who still sounded remarkably jolly. “I’m fine,” he said. “No, I’m not in a coma.

“I don’t know what’s going on or who put that out. It’s true that they found a fair amount of that rubbish inside me. I went to the doctors just in time as at one point things were not looking great. I’m not in the best of shape now but I’m okay. I’m certainly not in a coma.”

Had it simply been an erroneous, excitable report? Or was it another sign that the inquiry into Litvinenko’s death had turned into a game of cat and mouse in London and Moscow, with international relations at stake? Certainly British detectives were struggling in Moscow last week as they sought to interview witnesses and potential suspects. Among those they wanted to question was Andrei Lugovoi, another former spy who, along with Kovtun, met Litvinenko on the day he fell ill.

Late last week Lugovoi failed for the third time to see British investigators. One Russian news report said that he was suffering multiple organ failure from radiation poisoning; but his lawyer said his condition was no obstacle to being interviewed.

Yesterday, Kovtun, who has been interviewed by British police, told The Sunday Times that Lugovoi was being treated as an outpatient.

It was all beginning to look like Keystone Cops around the Kremlin, except that murder was involved and relations between Britain and Russia were deteriorating fast.

The Russian authorities announced that since their citizens had been poisoned they would conduct their own inquiry. They want to travel to London to pursue investigations there, including questioning the exiled Russian tycoon, Boris Berezovsky, who knew both Litvinenko and Lugovoi, and the dead man’s Chechen associate, Akhmed Zakayev, who has political asylum in Britain.

“There is no doubt that we will demand to question Berezovsky and Zakayev,” said a well-placed source in Moscow. “They both knew Litvinenko and they could hold vital information. Anyway, they are both wanted by Russian justice so I don’t see why we shouldn’t want to question them.”

Amid the diplomatic manoeuvring and tit-for-tat theories circulating over the killing, the stakes jumped when seven more people were found to be contaminated with polonium. They are all staff who worked in the Pine bar of the Millennium hotel in central London where Litvinenko met Lugovoi and Kovtun on November 1, the day he fell ill.

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