Kremlin is the 'biggest spy threat to London'

London: The Russian intelligence services, the prime suspects behind the murder of Alexander Litvinenko, have a network of more than 30 spies operating in Britain.

The sophisticated ring represents the greatest espionage threat facing Britain, Whitehall sources told The Sunday Telegraph.

The agents, equivalent to one in five of the Moscow government officials based in Britain, are known to be monitoring the movements and activities of Russian emigres and opponents of the Putin regime.

But they are also involved in a widespread operation targeting businessmen, parliamentarians and scientists in an attempt to steal commercial and state secrets. Only the United States, it is understood, has more Russian agents operating on its soil.

Whitehall sources claim that the agents are as active today as they were at the height of the Cold War, despite the fact that the Kremlin is now one of Britain's major allies in the war on terrorism.

The startling intelligence was presented last week to cabinet ministers at a Cobra meeting, where they are briefed on issues of national security. They were also told that Litvinenko, a former KGB agent, who died 10 days ago, was "most probably" murdered by "state sponsored" assassins, with the radioactive poison polonium 210 and that suspicion centred firmly on Moscow.

A source said: "The Russian intelligence services are highly bureaucratic and legalistic. There isn't a great deal of room for personal initiative, everything has to be officially authorised and signed off. And this murder would have been a highly complex operation involving many people, not one or two acting in isolation."

The revelations came as the Italian investigator Mario Scaramella, a friend of Litvinenko, was still being treated in hospital after also being contaminated with polonium 210 following their meeting at a sushi restaurant. On Saturday, he was showing "no evidence of radiation toxicity" but doctors said they were continuing to monitor his condition and further tests were expected.

A police source said: "The results may seem to suggest that Scaramella was an accidental victim but it is still possible that the perpetrators simply failed to do their job properly, or that Scaramella himself might have had another role."

Scaramella's name was one of five on a supposed "hit-list" of people allegedly targeted for assassination by the Russian intelligence services and a shadowy group of KGB veterans called Dignity and Honour, which is run by a Colonel Velentin Velichko.

'Brutal regime'

During the Cobra meeting, government officials and the police were briefed that Russia is being ruled by a "brutal regime" that regards dissidents such as Litvinenko and Boris Berezovsky, the Russian oligarch, living in exile in Britain, as terrorists. The Russian state is suspected of ordering the murder of five people in the past two decades.

Whitehall sources said that Russia continues to spy on Britain because of its "insatiable" appetite for other countries' state secrets. The main areas of interest include finance, the energy industry, defence, and electronics.

The threat is so severe that senior businessmen in companies such as BP and Centrica, have been warned by MI5 that they may be targeted.