A mid-week matinee. The theatre echoes with the thin, tinny whistling of the audience’s hearing aids. In the shadowed wings, there’s discussion of a much-loved and respected actor. The younger cast members are full of admiration. “I mean, a lovely man, darling,” whispers Diana Rigg as she breezes past me to make her entrance. “But breath like a serpent.”

What first met you was the presence. Diana sailed into a room like a galleon, draped in a stylish shawl, the blond bob framing those famous cheekbones. We were performing together at the Old Vic in Samuel Adamson’s version of All About My Mother, she as the actor Huma Rojo and I as her dresser, Agrado. It was a glorious, naughty time. She would eat a pork pie before every show and sit on the stairs, smoking furiously. “Exiled,” she would groan, waving a hand at the top floor rehearsal room. On the wall of that room, a framed photo of Laurence Olivier and Ralph Richardson in the same, happily haunted, space. Diana had been there before, of course, back in the early 70s, doing a disastrous Macbeth with Anthony Hopkins. Olivier had attended the first run-through, which was met with total silence. As the cast trooped out, Olivier beckoned to Diana. This was the moment. She awaited the sage advice from “Sir” that would unlock her Lady M. “I couldn’t help noticing,” said Olivier, “that you weren’t wearing a brassiere.”

As shown by the huge outpouring of affection following her death, to the public, Diana was forever Mrs Emma Peel. But the image of the astonishingly lithe, cat-suited Avenger, gun in hand, comma of fringe over the eye, could never overshadow what a terrific actor she was (though Diana always resolutely referred to herself as an actress). For all her triumphs, though – her famous Medea at the Almeida, her Martha in Who’s Afraid of Virginia Woolf?, her tragic Teresa Bond in On Her Majesty’s Secret Service – she always had ready access to a glorious vein of camp and self-deprecation. This was the Diana of Theatre of Blood, Evil Under the Sun and The Assassination Bureau: an absolute scream. In All About My Mother, the play within the play was A Streetcar Named Desire in which Diana had to be an improbable Blanche DuBois. In the original text, as her birthday cake is wheeled in she has to breathe: “When you reach… 30.” This was upped to “when you reach… 40.” She delivered the line at the dress rehearsal and, somewhere in the darkness, a stagehand laughed. Diana’s face dropped into perfect deadpan. ‘Oh, thank you.”

It was always pure joy to see her and when, a few years later, I was appearing in The Recruiting Officer at the Donmar with Diana’s brilliant daughter, Rachael Stirling, I hatched a plan. Rachael and Diana had never appeared in anything together. “What if,” I said tentatively, “I wrote an episode of Doctor Who for you both?” Rachael would come into work full of stories that I’d put straight into the script. Diana was recovering in hospital after a knee operation and Rachael had visited, finding her beloved Ma with her face turned to the wall. “You know,” she murmured, “I can’t bear to look at sick people…” The result was The Crimson Horror in which Rachael broke every heart and Diana chewed every bit of scenery as the monstrous Mrs Gillyflower, deploying her entire arsenal of outrageousness and her native Doncaster accent. I still can’t quite believe that the image of Dame Diana Rigg ripping aside her Victorian frock to reveal a prehistoric leech suckling at her throat was broadcast on primetime BBC One, but I remain so very glad that it was.

Earlier this year I was invited to see Edgar Wright’s new movie, Last Night in Soho, in which Diana is magnificent. Edgar and I spent the morning swapping stories about her, hooting with laughter, and then that very afternoon came the news that she had passed away. I rang Edgar immediately and he was then able to say how ill Diana had been and that he’d had to record one last line of dialogue from her bedside. She had been on sparkling form, Campari in hand, naughty and a true pro to the very end.

You know, the colloquial name for the Gillyflower is Dame’s Rocket. It’s entirely coincidental – I just liked the sound of the word for Diana’s Doctor Who villain – but in so many ways it was perfect for her. A glittering missile, full of fire and life – and gunpowder – who lit up the national imagination. They absolutely don’t make them like Diana any more. I shall miss her terribly.