For the past four years I have woken each morning and put on my metaphorical pearls before slipping into my office - and the mind of Miss Moneypenny.

It has been fun, and a challenge. Since I started “ghost writing” her private diaries, I don't think I have met anybody who doesn't know who Moneypenny is. In terms of name recognition she is up there with M, Blofeld and even 007 himself.

This undoubtedly owes much to Fleming's genius for picking memorable names (Goldfinger, Oddjob, Pussy Galore). But it's also down to Moneypenny herself. Of all his characters, she is the only one who is unequivocally likeable. Bond is cruel, M ruthless, most of the girls damaged dolly birds; Moneypenny alone is intelligent and loyal, a grown-up in a world of boy racers.

Fleming managed to create the essence of Moneypenny in remarkably few words. His descriptions of her, sprinkled through his 14 Bond books, are sparse: “M's private secretary would have been desirable but for eyes which were cool and direct and quizzical,” he wrote in Casino Royale. In Moonraker “Miss Moneypenny looked up from her typewriter and smiled at him. They liked each other and she knew Bond admired her looks”. And Thunderball: “Miss Moneypenny smiled cheerfully. She liked what she called the shot-and-shell days. It reminded her of when she started in the Service as a junior in the cipher department”.

Not exactly long on character detail - but enough for her first cinema incarnation, Lois Maxwell, to imbue her with a special spirit. When Maxwell was offered the part, she accepted “on the condition that I wouldn't have to play her with a pencil over my ear and my hair in a bun”. Instead, as she explained to me shortly before her death last year, “I decided - with a little nudge from Sean [Connery] - that, when Moneypenny was still in the secretarial pool, Bond invited her to spend a long weekend at his aunt's cottage in Kent. They had a most splendid time, but she knew that if she allowed herself to fall in love with him, he would break her heart. And he knew that he would never get his 00 number”.

That, said Lois, was the background to surely the longest screen flirtation in film history, packed with memorable scenes: “James, where have you been?” Moneypenny asks in On Her Majesty's Secret Service. “Much too far from you, darling.” “Same old James - only more so. Heartless brute, letting me pine away without even a postcard.” “Pine no more. Cocktails at eight at my place - just the two of us.” “Oh, I'd adore that ... if only I could trust myself.” “Same old Moneypenny: Britain's last line of defence.”

Singularly, among Bond women, Moneypenny was allowed the right to reply, even to trump the macho Bond, who usually admired women for their “splendid protuberances” and despised them for “hanging on to [one's] gun arm”. As Roger Moore explained: “Bond was quite willing to bed any female, but when it came to Moneypenny, although he enjoyed flirting with her, he treated her unlike any other lady - that is, with great respect. She brought humour, humility and class to Bond's world.”

Media academics have written treatises on what or who each of the characters represents. According to John Cox, a screenwriter: “Of all the members of Bond's SIS family, Moneypenny is the hardest to pin down. All the SIS team, I believe, represent Britain, specifically Britain during the war. M is Churchill, the leader. Q is the brilliant inventiveness of Britain. But Moneypenny ... she is the stoic spirit of sacrifice: she longs for the new world but she knows it is more important to stay at her post, to remain level-headed and sober, even when tempted.”

But not boringly so. When I took on Moneypenny four years ago, I was determined to be true to Fleming's creation. I wanted anyone who had read his books to recognise her character from my books - but also to relate to her in the present.

Moneypenny had to have a birthday, a family, a dress size, somewhere to live and someone to love; she needed memories of childhood, her first kiss and favourite holiday. Before I wrote a word, I had to know what she ate for breakfast and who cut her hair, as well as how she would react in any given situation.

I also needed to feel that I knew the world she inhabited - the Secret Intelligence Service in Sixties Britain - and to inch it a little closer to the real events that were hidden from the headlines. In this sense, I had an advantage over Fleming: most information about the secret dramas of the day was not in the public domain when he was writing. Even had he known the intergovernmental machinations behind the Cuban Missile Crisis, for instance, he would have been prevented by the Official Secrets Act from writing about them.

So, while the Bond books were highly coloured accounts of secret service action, Miss Moneypenny's diaries could be a bit more real, a little murky. While Moneypenny got to leave her typewriter for missions of her own, she was also embroiled in the desperate search for a mole buried deep in the upper echelons of the service, a search that brought with it suspicion, mistrust and, ultimately, tragedy.

I can't pretend that it hasn't been a romp at times. I managed to persuade myself that, to inhabit Moneypenny fully, I needed to go where she went, which provided me with wonderful opportunities for research trips to Cuba, Jamaica, Moscow, Miami and Berlin. I also met some spies: men and women who had been in the service at the time she hypothetically worked there.

And I gave her a niece, Kate Westbrook, to whom she bequeathed her diaries after her early death in October 1990, and whose experiences, as “editor” of the diaries, are interwoven with her aunt's adventures.

A year and a half ago, Casino Royale was released and, like millions of others, I loved it; as promised, it was a return to Fleming's Bond: brave, hard, cruel. But it had one gaping absence: Miss Moneypenny. Apparently her services have not been required for the forthcoming Quantum of Solace, either. I think that's a shame. I'm just delighted to have been allowed an opportunity to put on her pearls each day, and to keep her alive - between the covers of a book.

The Moneypenny Diaries: Final Fling by Kate Westbrook is published on May 1 by John Murray. Available from TimesBooksFirst for £16.19, free p&p. 0870 1608080; timesonline.co.uk/booksfirst

The Moneypenny Diaries: Guardian Angel, and Secret Servant are out in paperback.