The pat on the back from MI6's traditional adversary came from Sergei Ivanov, head of the Russian security council and adviser to President Vladimir Putin.

Asked by Argumenti i Fakti, a weekly newspaper, which country had the best agents, Mr Ivanov replied: "Ours, British and Israeli." American spies, he added, had too much money and were spoilt.

"British counter-intelligence has an excellent school and traditions, they prepare their agents very well," he said. Though MI5 is responsible for counter-intelligence in Britain, Mr Ivanov is assumed to be referring to the Secret Intelligence Service, MI6, which runs agents abroad.

He is also assumed to be referring to the MI6 training centre near Gosport in Hamp shire rather than Eton or Cambridge, the training grounds of such British double agents as Philby, Burgess, and Blunt.

MI6 can be particularly flattered since Mr Ivanov, like Mr Putin, is a former KGB officer.

The agency was unavailable for comment but Oleg Gordievsky, the former KGB officer who defected to MI6 in 1985, was willing to oblige.

He said the KGB regarded MI6 officers as "careful and imaginative, devious and dangerous". Unlike CIA agents, they were "courteous and polished".

The special relationship between the Russian and British intelligence agencies - sometimes described as "the great game" - began before the Russian revolution.

Mr Gordievsky said that while KGB officers were able to track CIA and other western agents in Moscow, MI6 was able to shake them off.

Mr Ivanov said the Americans "have too much money. This leads to an impression that everything in the world can be bought and you don't have to use your head".

In a foreword to a booklet, National Intelligence Machinery, published by the Cabinet Office, Mr Blair said: "Secret intelligence gives the government a vital edge in tackling some of the most difficult problems we face." The intelligence agencies "serve this country well. We owe them a great deal for their unsung work," he said.