When a 90-year-old retired Foreign Office secretary died recently the secrets of her Cold War past could finally be revealed.

Valerie Pettit may have seemed to her neighbours in the village of West Clandon, Surrey, as an ordinary churchgoing elderly woman, but with her death came revelations of her central role in organising the escape of a Russian spy.

Pettit was the architect of Operation Pimlico, an operation that smuggled KGB colonel Oleg Gordievsky out of Moscow when he was betrayed by a disgruntled CIA officer in May 1985, The Times reported.

Valerie Pettit (right) may have seemed to her neighbours in the village of West Clandon, Surrey, as an ordinary churchgoing elderly woman, but with her death came revelations of her central role in organising the 1985 escape of Russian spy Oleg Gordievsky (left)

Seven years earlier, as deputy to the head of MI6's Soviet Operations section, a 48-year-old Pettit devised a cunning way for British intelligence officers to get Gordievsky - recruited by MI6 in Copenhagen in 1973 - out of Moscow if he was ever under suspicion.

If Gordievsky found himself in trouble he was told to arm himself with a Safeway shopping bag and stand at a certain central Moscow street corner at exactly 7.30pm on a Tuesday.

An MI6 officer would acknowledge the call for help by walking close by with a green Harrods bag while eating a British chocolate bar - a KitKat or Mars Bar.

Pettit (second right) stood next to Gordievsky (left) as they stopped for a photograph on their way through Finland during the daring escape

Russian spy Gordievsky, widely acknowledged to be the most valuable secret service mole at the heart of the KGB, with his ex-wife Mrs Leyla Gordievsky

The next stage of the plan would see Gordievsky meet MI6 officers at a layby in the woods south of the border with Finland.

Covert surveillance photographs of Gordievsky taken by the Danish intelligence service PET during his postings to Copenhagen

The corner was monitored by agents every week for seven years, even when Gordievsky was called over to work from the Soviet embassy in Britain in 1982.

One MI6 officer, years later, revealed he never wanted to see another KitKat because those monitoring the spot got used to carrying around a chocolate bar just in case.

For three years Pettit arranged weekly meetings with Gordievsky at a safehouse in Bayswater, London, where he spilled the deepest secrets of the Russian intelligence during the darkest period of the Cold War while enjoying beer and smoked salmon.

But in 1985 Aldrich Ames, an irate CIA officer, called the KGB in Washington.

MI6 had shared intelligence with the CIA, concealing its source, but the US had carried out its own investigation to identify Gordievsky.

Godievsky was summoned back to Moscow (pictured) in 1985 under the guise of being made the head of the KGB in Britain. As soon as he arrived he realised he had been rumbled

He was summoned back to Moscow the next day, under the guise of being made the head of the KGB in Britain. As soon as he arrived he realised he had been rumbled.

Gordievsky in his student days at Moscow's elite Institute of International Affairs where he was first recruited by the KGB

A packet of pills to keep him alert and a pouch of snuff to disguise the smell from Russian sniffer dogs, given to him by Pettit, meant he was able to evade surveillance and set Operation Pimlico in motion.

On July 16, 1985, a man could be seen standing outside a bread shop on Kutuzovsky Prospekt, the wide avenue running from the centre of Moscow, at 7.30pm.

Some 20 minutes later he was passed by a man holding a Harrod's carrier bag and eating a Mars Bar.

Four days later Gordievsky met two officers and their wives at a point south of Vybord where he was bundled into the boot of one of two cars and covered in a heat reflective blanket.

The blanket would stop him being seen by infrared cameras as the car passed across the border into Finland.

Gordievsky (pictured in 1976) continues to defy Moscow from a safehouse in Britain. He escaped in the boot of MI6 officer's car in July 1985

For years these covert surveillance photos were the only images available of him

But when they got to the border sniffer dogs detected Gordievsky in the boot of the car and began circling. The two officers' wives were forced to deploy tactics of distraction.

Aldrich Ames, a former CIA agent who became a mole for the KGB

One opened a bag of cheese-and-onion crisps while another dropped her child's dirty nappy under the boot to disguise Gordievsky.

Once the car reached safety the officer who was driving put Sibelius's Finlandia into the cassette player, and turned it up to full volume.

Just minutes later the cars parked up in a clearing in a forest where Pettit was waiting.

'She opened the boot to let me out,' wrote Gordievsky, now 81 and still living in a safehouse in Britain. 'She was the first person I saw as a free man.'

Gordievsky seized both her hands and kissed them. 'I was betrayed,' he told her.

He sat in the back of a Finnish rental car as Pettit drove them north for the Norwegian border.

Gordievsky, a keen badminton player, and right in his KGB uniform, switched his loyalty from Moscow to the West and took on the dangerous role of a double agent

According to one officer present Pettit was visibly moved, 'her expression a mixture of recognition and love', despite usually disapproving of emotional outbursts.

Gordievsky described Valerie as a 'perfectionist' who 'always showed me great kindness and a lot of patience'.

During her retirement Pettit lived with her mother and sister in Surrey.

Born in 1929 near the Lord's Cricket ground she was the eldest daughter of Charles Pettit, a solicitor who was badly wounded in the Second World War, and Valerie Douglas, a Scottish dancer.

Whenever the churchgoer was asked what she did during her career she answered that she was a Foreign Office secretary and then moved the conversation on.

In The Spy and the Traitor, an account of the Gordievsky case by the Times writer Ben Macintyre, she was disguised with the pseudonym 'Veronica Price'.