The composer John Tavener, 53, started his career as a flamboyant member of the Sixties classical avant-garde, recording on the Beatles' Apple label. In 1977, he joined the Russian Orthodox Church, a move which has deeply influenced his music ever since. He lives in Sussex with his two children and his second wife. The actress Mia Farrow, 52, first became famous in the 1968 film 'Rosemary's Baby'. In 1980, after brief marriages to Frank Sinatra and Andre Previn, she met Woody Allen. They were together for 12 years, but broke up acrimoniously - and famously - when he began a relationship with one of Farrow's adopted daughters, Soon-Yi. Farrow now lives with seven of her children in Connecticut

JOHN TAVENER: I first met Mia in the early Seventies when she was making her first British appearance on stage. It was in a play called Mary Rose and I was doing the music for the production. I remember going into a Covent Garden pub and she came in and made a bee-line for me. I made a bee-line for her too - which isn't a thing I normally do, because I'm very shy. But there was something very special about her: she had a certain aura. All I can remember about the first meeting was the pace at which she came towards me - very fast; there was no side-tracking.

Soon after that we went up to Manchester - Mary Rose was playing at the Exchange. I remember one night we stayed up extremely late, and Mia said she wanted to go and play the organ in a local church. She ended up waking a priest at about two in the morning, saying: "I want to hear John playing the organ." He said - basically - what the hell are you doing here at this time of night?

We realised early on that we had a spirituality in common. With her it's childlike and rather fierce. She's very transparent and goes straight to the point. She seems to have a purity of heart that comes from the faith she's got. Mia's not interested in earthly knowledge. She's not really interested in earthly things at all. One feels, when one's been in her company, that you've had a cold shower and feel much better for it - even if you do feel rather exhausted because she does talk and drink on rather an exhaustive scale. She loves red wine.

I don't think I've ever had a mundane conversation with Mia. In fact, she talks at a fairly high level all the time - she's also got quite a savage sense of humour. And she'd never tell a lie - she wouldn't know how to. It all comes straight out. I admire her honesty and her complete lack of pretension.

When Mia is present, things can go in a curious direction. I remember having dinner with her in Sussex, and the man who ran the restaurant was very petit bourgeoisie. We may have been holding each other or whatever, and he came across and said: "I know who you are and I'm going to write to one of the tabloids." Typical of Mia, she went up to the blackboard where the menu was written, rubbed it off and wrote: "Don't eat here." Then she giggled.

Although we were always just good friends, the tabloids soon started to get onto it. Early on, I remember various tabloid people coming to my house. Mia can be naughty. When there were various scandals going on with Andre Previn, I think she had the insane idea of wanting to blow up the Daily Mail. She literally got as far as planning, with a friend of mine, who'd go and put the bomb there. Of course, one had to say: don't be so ridiculous. You can't do this. It could have been just naughty humour - certainly she wouldn't do anything like that now.

When she got involved with Woody Allen, I was holidaying in Cornwall and got a phone call from her, asking if I could come for dinner at Claridges that night. That's typical of her; very last minute. She talks an awful lot about Woody; the only person who seems to have deeply upset her in her life, as far as I can understand, is him. She doesn't have an ounce of bitterness in her. She's terribly pure. But I think she does really believe he's evil. I've never met him - I think Woody was enormously jealous of meeting anyone she knew. I don't think she's changed through it all, although she's not quite as childlike as she was. There was a sort of effervescence about her before; a mad intensity. Now we do have slightly more sober conversations.

I last saw her in New York in the middle of that terrible trial, in what you'd think would be an unbearable situation, and she was just exactly the same. I remember going to her flat and one of her children answered the door and there she was, looking exactly as she always does. She doesn't change at all. She never puts on make-up and she wears nice but very ordinary clothes. There's nothing film starry about her at all - I love that because she's such a natural person.

That evening was one of my most affectionate memories of her. Again we drank lots of red wine; we went to a Mexican restaurant. She's not a person who makes too much fuss about what's going on in her life. This was when the trial was at its peak and people were coming up to her in the street saying: "We're with you." Yet there was no sign of stress on her face at all or in her manner. I remember it as a day of sunshine; great calmness and peace; that's how I felt when I came out.

I've never lost contact with her. At the moment we tend to fax each other maybe five times a week, leave it for a few months and then start again. I tend to write about spiritual things that connect to her in some way and she faxes me similar things back. We might discuss my work - I'm writing something for her in which she's going to act. It's a pantomime/comic opera about the after-life.

We do talk about God, but not in an intellectual way. She talks about her mother sometimes; Mia fears that when her mother dies she'll be an orphan - that's about as near as we get to mundane conversation.

I'd say she's found contentment now. Is she happy? Happy isn't a word I'd ever apply to her. I think she probably believes, maybe the same as I do, that happiness isn't something you experience in this world. You can be joyful for periods of time; but "happy" suggests a type of complacency, and Mia's certainly not complacent.

I think we're similar to each other, but not in a superficial way. I think we've always thought like brother and sister. It's difficult to explain our relationship. Being with her is like being drunk without drinking. It's like being slightly inebriated; inebriated by each other. It does sound like a description of being in love; it's a form of love and I do love her.

MIA FARROW: I remember first seeing John in a grungy hall, rehearsing Mary Rose, for which he wrote the very beautiful music. He walked in wearing this beautiful white suit. I thought I'd never seen anyone who looked quite like him before. I thought he was very striking looking. I just always wear my jeans and my T-shirt - then and now. But John was in this pure white suit that was almost Edwardian, and he had hair way down his shoulders as well as a suntan. That was mystifying because I'd been living in England and didn't recall having seen the sun for a few years.

Then we all went to the pub for lunch. I recall rushing up to him when he came in because I thought the score was so beautiful. I remember he wasn't very chatty but everything he said was meaningful. I'm not really very chatty either but I can sort of wing it better than John if I have to.

As soon as we met, we got to know each other immediately. We understood everything we needed to know right away. We were very young then - in our twenties - and I didn't realise how rare it is when that happens. Now that I've known John most of my life, I know how unusual our friendship is.

I think of John as my spiritual twin; my soul mate. We do talk a lot about spiritual things and have an identi- cal response to everything. We have a shared perspective which gets us laughing; sometimes without saying anything at all. I almost don't really need to talk when I'm with John because we're communicating anyway. It's so perfect; we've never had a disagreement or anything approaching an unpleasant or awkward moment, and I don't think we ever would. He's got precisely my sense of humour. I find it easy to make him laugh and he laughs a lot at me. His observations are very funny and he has a funny way of putting things.

Once we were going somewhere in his car which was a big Rolls-Royce. That's where we differ on a superficial level: John would choose a Rolls- Royce and I would choose a Land Rover. I'd be wearing jeans and he'd be all dressed up. Anyway, we were going somewhere in heavy traffic and John was just so exasperated. He had no tolerance for it and wanted to be somewhere else. So we just got out of the car and left it stopped in the traffic. I remember him stalking away in one of his fabulous white suits, very tall with long legs. I always forget to ask him what did happen to that car.

John has always been a supportive friend. I feel it would be an alien world if he wasn't in it because people are so mystifying. He's met my children - he's great with kids. I don't think he ever met Woody, but he should have. John's very perceptive; maybe he could have warned me, but I doubt that he'd have seen it either. John wouldn't have an understanding of someone so unlike himself. Certain people are unfathomable to John and to me too. I made the assumption most of my life that people are like me; John's entirely like me.

It's almost like coming home when he and I are together. He's absolutely truthful and direct. We don't have to waste a lot of time telling stories - he's not anecdotal like a lot of people. There's just an immediate connection.

When I was living in England in the Seventies, we would see each other pretty regularly. The people I've met through him I like very much too. When we see other people we do make every effort to include them but they're not usually on the same level. I think they can feel quite left out - except for John's godmother, who we used to visit a lot in Sussex. We used to have tea in her garden and the three of us would sit around laughing. She was great. I loved her immediately.

I would like to see more of John, but we're always communicating in some way. I know he's thinking of me or praying for me, so whether we're actually together or not is almost irrelevant. It's just so much fun: we speak all the time on the phone and he sends me faxes - though I can never read his writing. I have to ring him up and say, "What?", and then we get talking. We go through phases of ringing each other a couple of times a day, then a month will go by and there'll be a letter or fax that will trigger a daily communication.

Some of his faxes are wonderful - I should give them to him one day because he might want to publish them. They're such revelations of his yearning for God and all the things he's confronted. My nine-year-old son isn't unlike John - one day he disappointed himself in some silly way and said: "Oh, it's so difficult being a human being. You have to weed every single day." And I thought that was a great met-aphor - John's certainly done that.

I don't know what our relationship would be if it weren't platonic. Our timing was never such that we could become involved. It was probably in the air but we never could have because John would never be unfaithful - I wouldn't either. He was always married or I was and we missed the moments in between. He had a couple of Greek wives and they were always very bossy - I don't know what that was. But we have that fantasy of ending up with each other if we get to 100 years old. We have such a shared vision of everything; we would be very well suited. He knows that I'd take care of him or be there in any sense if he needed me. Nobody really understands our relationship at all - it's not what anybody would think. All these years he's been so close to me and it's just a real comfort to know he exists.

John Tavener's 'The Whale' will be performed by the London Sinfonietta on 24 January, at the Queen Elizabeth Hall, SE1.