Last week, prosecutors began a formal extradition process of former KGB agent Andrei Lugovoy, the man suspected of killing Mr Litvinenko.

The Attorney General has told Russia's chief prosecutor that Lugovoy must face trial in the UK.

In a face-to-face meeting with chief prosecutor Yuri Chaika, Lord Goldsmith said he expected the Russian authorities to co-operate.

Meanwhile, a high-ranking Russian politician appeared to suggest Russia could extradite Lugovoy to Britain in exchange for Boris Berezovsky, an exiled tycoon long sought by Russia.

Lawmaker Vladimir Vasilyev, who heads the security committee in the lower house of parliament, said that Russian law did not allow for the extradition of Lugovoy, but he appeared to indicate that the question was open to negotiation.

However, a spokesman for the Crown Prosecution Service dismissed the idea.

Mr Berezovsky fell out with Russian President Vladimir Putin within months of his 2000 election and fled to Britain, where he was granted citizenship.

Berezovsky and his supporters maintain that Russia's attempts to return him to the country for trial are aimed at punishing him for his criticism of Putin.

Lugovoy was charged with Mr Litvinenko's murder last week. The exiled former Russian spy was poisoned with radioactive polonium-210 in London in November last year.