She’s retired now, of course, but Dame Stella Rimington cut an imposing figure tonight as she stood in front of a packed house, talking to us about the ground-breaking career she forged in intelligence, culminating in her appointment as the first female – and publicly named – Director General of MI5.

And yet, this best-selling novelist told us, her dream job would have been to work here at the National Archives: Dame Stella is, after all, a trained archivist – not to mention a Liverpool alumna like me (a piece of information that made me very happy). She did, in fact, apply for a job at the NA – only to be told that she “wasn’t intellectual enough”. Instead, a placement in Worcester beckoned.

What a different world we inhabited then. Dame Stella married a civil servant in 1963 and, when John was offered a posting in New Delhi, gave up her job to go with him. “As children of war, we were delighted by this opportunity”, she recalls. “But I was very much a diplomat’s wife”. And the life of a diplomat’s wife was not particularly exciting: you couldn’t work, and were expected to participate in coffee mornings, jumble sales and amateur dramatics.

There were some interesting moments, travels to Pakistan and Afghanistan among them. And then, just as Dame Stella was starting to get bored, she was asked if she’d like to become a spy.

Well, sort of. A New Delhi-based M15 agent, tasked with helping Commonwealth security, hired Dame Stella as his part-time secretary/typist. This was “a hugely exciting time to be working in Intelligence in India”. The country was at the forefront of the Cold War and “full of spies”. Dame Stella was asked to identify them, inadvertently making herself and her husband the target of KGB recruitment.

Having returned to the UK, Dame Stella successfully applied for a full time role with MI5, only to discover that it was run entirely by men – who viewed women as second class citizens. The entire service operated in a “paranoid” atmosphere, which worsened after the defection, in 1971, of a KGB officer from the Soviet Embassy, following which the British government expelled 90 Soviet diplomats discovered to have been engaged in active espionage. “There was a sense of being got at; a real sense of danger”, mused Dame Stella. “Remember: I was working with people who had known, and felt betrayed by, the Cambridge Five”.

Said paranoid colleagues included Peter Wright, author of 1987’s notorious ‘Spycatcher’. In cahoots with CIA, he was convinced that all Western intelligence had been infiltrated by the KGB – to the point of investigating a former MI5 Director General, Roger Hollis, as a spy.

Again, these were such different times. The remit of MI5, Dame Stella told us, remains the same: to protect the country against serious threats by gathering secret intelligence through various sources – but the way in which it does so has much changed. Back in the day, steaming open letters, following people on foot and drilling holes in walls for microphones and cameras were the best weapons at our disposal.

One element has remained the same – and that is the use of human sources. An intelligence service like MI5 will target a person deep in the heart of a particular organisation or country that’s perceived as a threat, and try to persuade them to change sides. “People become disillusioned – and that’s what you’re looking for”, Dame Stella told us. “Unlike films and TV, it’s rare that money change hands – and blackmail is never used, as people susceptible to that tend to be unreliable”.

The two tier system within MI5 did, thankfully, begin to crumble with the advent of women’s lib and the introduction of anti-sex discrimination legislation. With female employers beginning to ask more questions, the supply of men “began to dry up”. A “quiet female revolution” was taking place, beamed Dame Stella – one that was “elegantly done, but firm”.

Progress, however, remained slow. In the mid ‘70s, Dame Stella was the first female MI5 employee to be sent on a ‘Recruiting Resources’ course, which involved going into a pub and, using a cover story, learning what you could about everyone in the pub – following which, your cover story would be blown while you were observed to see how well you dealt with the embarrassment.

Unluckily for Dame Stella, she was designated “a sleazy dump of a pub, near Victoria station, frequented by men in dirty macs”. Mindful of her duty, she began chatting up one of the male customers – much to his delight. “I nearly got thrown out for soliciting”, Dame Stella chuckled.

Humorous, yes – but also wearying. Dame Stella “nearly gave up”, but battled on, understanding the value of diversity. “I knew that MI5 was ignoring the talents of one third of its staff”, she recollected. Only gradually did the service come to understand the importance of women to its profession.

In the meantime, counter-espionage remained a “slow, careful, cautious activity”, based around tracking down intelligence officers in London, arresting and then prosecuting them. It did often feel, Dame Stella agreed, like a John le Carré Cold War novel.

For their part, the KGB regularly tried to infiltrate legitimate pressure groups, including our trade unions, in an attempt to sway them to the Russian agenda. This presented MI5 with a particular problem: how to stop it without appearing anti-pressure group?

As we transitioned into the 1980s, terrorism presented MI5 with a completely new challenge. MI5 itself had to change in nature and work much more closely with the police. Traditionally, it had kept them at arm’s length: “But intelligence is not evidence – and evidence is what you need to prosecute.”

Gradually, Eastern Europe and the Soviet Union “began to shake”, as Mikhail Gorbachev implemented reforms. Surprisingly, MI5 noticed some of this “but we weren’t well enough connected to understand what was happening”. The KBG began to split into old and young factions, with the latter wanting to change and reform.

Following a 1991 meeting between the then-Foreign Secretary Douglas Hurd and Boris Yeltsin, during which Yeltsin asked for British assistance in democratising the KGB, Dame Stella and several of her colleagues travelled to Moscow. It was, Dame Stella recalls, “a very bizarre experience”. Met by men in long coats, the team stayed with the British Ambassador and attended meetings in Lubyanka. There, they talked to their Russian counterparts about intelligence in a democracy. Asked to sign a co-operation agreement, the British team was trailed while out sightseeing.

To this date, Dame Stella mused, not much has changed – and she views Putin as a “cold war warrior still operating as though the Cold War is going on”. Once again, Russia seems to view the West as its enemy.

Home from Russia, Dame Stella was told that she was being promoted to Director General of MI5 – a role for which she had not applied – and that, for the first time in history, the DG’s name would be shared with the public. No photos, the government agreed, would be published of her, due to the ongoing IRA threat.

After she issued a statement saying how delighted she was, the media set about discovering Dame Stella’s identity. Inevitably, it didn’t take them long: ‘Housewife Super Spy’ screamed the first headline.

With the Cold War over, Dame Stella decided it was important the work of this country’s intelligence service was understood – and, accordingly, gave the 1994 Dimbleby Lecture. One journalist’s response was to state that Dame Stella had very good ears, which must come in useful in her line of work.

Sigh.

Undeterred, Dame Stella proceeded with her “openness” strategy – which had some notable successes, although the Cold War image remained hard to shake off. Bizarrely, it was James Bond who “came back to bite MI5”, after Judi Dench began playing the role of M’, looking uncannily like Dame Stella.

Our intelligence services have continued to become more and more open and, these days, regularly engage with the public. Dame Stella retired in 1996 and went on to become a best-selling novelist – and highly sought-after an after-dinner speaker. Modest about her not-inconsiderable achievements, and blessed with a great sense of humour, it’s not hard to understand why.