A Bexleyheath grandmother who lived a quiet life in a leafy street was the KGB’s most prized spy, it has been revealed.

Melita Norwood passed secrets to the Russians for decades after being recruited in 1935 by a former correspondent for the Soviet news agency TASS.

The grandmother was 87 and living in a semi-detached house in Garden Avenue when she was first unmasked in an explosive book in 1999.

But it has now been shown just how important she was to the Soviet Union during the Cold War after the first batch of notes copied from the KGB archives by a defector to the west were made public.

Vasili Mitrokhin’s documents show the ‘granny spy’, as Norwood became known, was even more highly prized than infamous traitor and member of the Cambridge Five group of spooks Kim Philby.

Codenamed ‘Hola’, the communist party member and secretary of a British research association working on nuclear reactor technology passed on reams of documents on metallurgy which were useful for Russian armament manufacture.

The files describe her as "a loyal, trustworthy, disciplined agent, sought to bring maximum benefit.

"She passed on a very large number of scientific and technical documentary materials that are practically applied in Soviet industry."

The first 2,000 pages of Mitrokhin’s files to be released reveal Norwood was awarded the Order Of The Red Banner Of Labour for her service to Soviet intelligence.

Not only that but she was paid a lifetime pension of £20 a month in recognition of her "many years of excellent work".

Professor Christopher Andrew’s book on Mitrokhin’s files The Sword and the Shield first exposed Norwood.

He told a national newspaper: "At that time, security agencies were somewhat chauvinistic so to prefer a woman to Philby at that time, shows just how important she was to them.

"It is unlikely she realised the significance of much of what she was passing on but there is no doubt from these documents that the information she passed on was extremely useful to the KGB."

Norwood was never prosecuted because the attorney general deemed it "inappropriate" and she died in 2005.