I don’t know how I got her number, but I do remember it wasn’t difficult. I wanted to write about Barbara and Sid. I needed her permission.

“Hello, darling, it’s Barbara here. What’s all this about, then?”

“I’m writing about Kenneth and Sid, and I’d like to put you in the middle of ’em,” I porky-pied.

“That sounds lovely, darling. You’re not going to do ’em in, are you?”

“No, I’m not.”

“No, cos they were lovely. You go right ahead, then.”

“Obviously, you can read what I write once I’ve written it.”

“Oh no, darling. I trust you.”

(We’d never met.)

“Seriously. I’ll need you to read it.”

“All right, darling. Good luck with it.”

So I wrote it, and I sent it to her, and two days of ominous silence were broken by a phone call.

“Hello, darling. It’s Barbara. It’s lovely, darling. I love it. But tell me one thing?”

“What’s that?”

“How did you know?”

“Well, it’s common knowledge.”

“Not me and Sid – the other things. How did you know about the pillow?”

“Guesswork,” I replied.

Which was true. That she cuddled her pillow to sleep before she met the redoubtable Scott Mitchell (her third husband) was, it turned out, a serendipitous bit of imagination. It wasn’t hard to have imagined Barbara because Barbara turned out to be everything I’d hoped, and you’ll find no one in the business who discovered otherwise.

From that phone call onwards, she was wonderfully generous and supportive to me throughout the incarnations of my play Cleo, Camping, Emmanuelle and Dick and, beyond that, popping up on opening nights with a cheerful grin and those sparkling myopic peepers, beaming up at the faces that were invariably a foot above her own. Her friendship was a benediction.

The actor David Streames remembers spending a day with her a few years ago. “By the time we said goodbye, we were old friends.” And that was one of her abiding gifts: wherever she was, if you were there too, she was there for you. She was approachable, available, open.

My fondest memory of Barbara is sitting in an Italian restaurant with her, her husband Scott, and Samantha Spiro, who was about to depict her on stage. Sam was drinking Barbara in, and Barbara was happily topping up the glasses.

“What about wigs?” said Sam, who shared Barbara’s sense of mischief and had judged correctly her willingness to have her personal space invaded in the pursuit of art and good gossip.

“Oh, darling, I get through about six a year. It should be more really. They tend to go a bit sticky-up at the fringe, but look …”

Barbara wound a lock of blond hair around her index finger and gave it a sharp tug, discarding the wisp on to her napkin. “I’ll get another few weeks out of this one.”

Barbara was humble, cheeky, funny and self-deprecating. She was also deeply loyal, fathomlessly gentle and quietly supportive. I never heard her say a bad word about a single soul.

Comedy writer Meryl O’Rourke reflects that, in the 1970s, Barbara was “our Beyoncé, if being in charge of your sexuality means anything. On screen, she was young and alpha, dressing purposely to show us her sexual power, being the one to choose, making the first move. Knowing and willingly sexual. That’s not sexist; the women were the leads.”

In O’Rourke’s opinion, the only sexist thing about the Carry On films were the minuscule fees. There’s little argument that Barbara wore it well – and didn’t wear it even better. Yuk, yuk, yuk. Oh, Sidney!

She was also sentimental. She carried her madcap past lightly but with great care. She understood her history was precious, not only to her but to every soul who smiled in her direction with the joy of recognition. She survived the pratfalls and indignities of her beloved showbusiness like the genuine trouper she was. Few actresses have been as comically objectified, but far fewer have found the dignity innate in that complex role. We never laughed at Barbara; we always laughed at the men she distracted, entranced and inevitably trounced. Because Barbara, for all the ditzy, blousy notes demanded of her, played the instrument of her loveliness simple and strong.

And then, as the decades that might have forgotten her began to pass, she changed direction. Some actors change gear, Barbara changed the entire gearbox. Playing the Fairy Godmother is all very well – it keeps the wolf from the door and the smiles in the air – but I suspect it can be less rewarding than it is demanding, those three-a-day panto seasons of enforced cheer.

And so Barbara went legit. And wisely so; she remade herself by staying true to herself. She let every English rose and giggling ribbon we’d pinned on her fall away and let us find the person we are all so glad not to have missed. The compassion shone through, and, as always, the dignity. She accepted her iconic status and grew so … graciously. She was the diminutive soul who stood tall.

I wrote these words for Kenneth Williams: “You know why you love her, Sid? She’s vivid. From the Greek. Vivace. She’s vivacious; and she vivifies. She pertains to life. She’s somehow got the hang of it, unlike you and I.”

So, back at the turn of the century, we are filming Cor, Blimey!: Barbara has suggested she play herself in the final scene. Quite firmly suggested, though my arm had needed little twisting. We walk together across the lot towards the derelict caravan in which we’ll be shooting. Suddenly, she grips my arm. It’s vice-like. She seems unsteady on her feet.

“Are you OK?”

“Oh, darling. I’m nervous. All of a sudden. I’m really nervous.”

“Just be yourself.”

“Well, that’s it, isn’t it; you silly sod. That’s what’s difficult.”

“Well, you’ve done it quite well for 60 years.”

She pauses, thoughtfully.

“You know what? If I say so myself, I bloody well have.”

• Terry Johnson wrote the stage play Cleo, Camping, Emmanuelle and Dick, and the film Cor, Blimey!