Stevenson has just been voted all-time favourite reader by listeners of Radio 4's Woman's Hour, for her reading of Anna Karenina. This month, we are due for another treat: Stevenson reading Madame Bovary. She has run a long way since the legendary Vanessa Whitburn saw her at Stratford in her first RSC sea- son and offered her the chance of that first dash.
Her devotion to radio began when she was about 14. She is still addicted, listening far more than she ever watches TV, and experiencing a positive thrill every time she switches on. "I mean, this morning," she adds, "I turned it on and there was a programme all about whistling! I just love it."
She readily agrees with Tom Stoppard's remark that radio is the best medium for drama because the scenery's so good. She would like the acting to be so natural that a casual listener might not know whether it was real conversation or a play.
She has always felt like that. Her second performance was also for Whitburn, this time in a full-length play: "I turned up having learnt the whole script, much to the scorn of the old hands. There's a received wisdom in radio drama that says you have your microphone here, your script there, and off you go. But it's a killer if you don't engage with other actors, look at them and listen to them. If people come in with a completely rehearsed and prepared performance, they don't allow for what might come at them, might spontaneously just happen, to turn it into a live - a living - event".
She also likes to do her own sound-effects. "Your physical actions affect your voice, the way you talk, and your timing: I couldn't conceive of acting without properly inhabiting the role." Anyone who heard her transfixing performance last autumn in Gaslight will agree that she is totally possessed by her roles.
Talking energetically in her warm kitchen in north London, she makes great use of her hands and, particularly, of her lovely, mobile face. To be deprived of these visible assets must be a handicap? Well, no. "The microphone can pick up amazing things," she insists, in a burst of enthusiasm; "the spontaneous, the unexpected, the lateral, the instinctive ... and it also picks up phoneyness and effort. It seems to me that the voice holds everything in it. It holds unspoken thought in it. It holds buried fear in it; it holds secrets. It's connected to the brain, to the heart and to the instinct: it's as expressive as a face and it reflects, as eyes do - but only if you're not completely controlling it".
This willingness to let intuition rule contributes to her success as a reader - coupled with preparation. She always tries to read the books in their entirety before she starts recording. "Anyway," she admits, "I like to fiddle with abridgements, because there are some bits I just can't bear to leave out. Di Speirs [her producer] and I spend a lot of time in the studio, just sneaking bits back in."
She's an old hand at the classics, having read all of Jane Austen for Naxos and the Brontes for Penguin, but she has a particular fondness for Anna Karenina; "It was a joy, the best novel I've ever read. I couldn't believe the infinite wisdom of Tolstoy". She identified so closely with the heroine that she found some parts almost impossible to read: "I couldn't do the scene where she comes back to see her son: I kept breaking down." She herself has a three-year-old called Rosalind. "You know, as soon as you've got a child you just can't cope with anything about leaving them or losing them."
But she knows that won't do. "It's no good to the listener if you're emoting like mad. You're just a vessel for the author: the challenge and difficulty of reading books on the radio is not to lay your own tone on what you're reading, but to find the quality of the relationship the author has with his or her material."
She loves the diversity of her life. If, in some horrible authoritarian state, she were forced to choose between performing on stage, screen or airwaves, she would probably opt for the stage, poorly paid and infuriating as it can be. Recently, she completed a European tour of short Samuel Beckett plays (to be seen in London this autumn) and was delighted by the variety of audience reaction. Radio audiences can't offer a performer an immediate response, but they can write - and they do. After the broadcast of Anna Karenina, she received at least as many appreciative letters as had been sent to her after the release of Truly, Madly, Deeply.
When asked to explain her unparalleled popularity as a reader, she resorts to comparison. Rosalind loves story-tapes, and her mother has discovered some that they can hear again and again. Alan Bennett reading Winnie the Pooh is one; another is David Davis doing the Just So Stories. "He doesn't colour and sing-song and describe what he's reading. He's hypnotic and steady and fantastically rhythmical to listen to, like music, and he never interferes with the material, or interprets it. There's a way of reading the words that's not about lack of commitment - far from it - but about trusting the listener."
It is just this line that Stevenson has taken with Madame Bovary. Startled by the suggestion that Flaubert might have been misogynistic towards his heroine, she sets about a spirited, sympathetic defence: "Emma Bovary is forced to live a life of unmitigated tedium. It is horrendous, hidebound and bitter. Certainly, at times her behaviour is unforgivable, but Flaubert puts her in a large social, political and economic context, so you are brought to an understanding of her. All the time, there are clues about her behaviour, which we, at the end of the next century, can pick up."
She is dismayed by the news that the Woman's Hour serial is to be replaced by a new soap. "It's such an odd decision, when people clearly love to be read to and there is such a drive to improve literacy. I can't understand this notion that we want less and want it more rapidly. People might never get round to reading, say, War and Peace, for themselves, but if they hear a few episodes, they can feel that they have; they will realise it's not intimidating. And besides, great books pick you up and transport you far away - and I don't think anyone's transported by soaps."
And then little Rosalind appeared and politely requested, and was granted, the full attention of the very best reader of stories in the business.
'Madame Bovary': 'Woman's Hour' (R4), from Mon & BBC Radio Collection, ISBN 0563382988, pounds 12.99.