Boris Berezovsky, the Russian billionaire exiled in London, said on Wednesday he had been warned by British police of a plan to murder him – but the UK government refused to comment on the allegations, suggesting it did not wish to worsen already fraught relations with Moscow.

Mr Berezovsky, an implacable opponent of the Russian president Vladimir Putin, said he had been advised by British police to leave the country last month for his own safety because he was the target of a planned assassination.