Russia’s top prosecutor has told Scotland Yard that it must let the Kremlin’s investigators question critics of President Putin living in Britain before British detectives can return to Moscow to finish investigating the murder of Alexander Litvinenko. Yuri Chaika delivered his ultimatum as he revealed that detectives have asked to visit Moscow again to question a number of suspects about the murder of the former spy...The chief prosecutor made it clear that there was no chance that British police would be allowed to return to Moscow before his team have finished their work in Britain.

The Russians have asked to question up to 100 people. A number are reluctant and have asked British police for firm assurances about their safety...Last night Alex Goldfarb, a close friend of the tycoon, said that Mr Berezovsky believed that the Russian investigation was “a farce” and he was fearful that he could be poisoned while being questioned.

As he has asylum here, he does not have to meet the Russian officers.

“All of this is an exercise in obstruction,” Mr Goldfarb said. “He will speak if the security is provided — if the British guarantee there is no polonium.