If anyone appeared to live a charmed life in the Sixties and Seventies, it was the model Pattie Boyd. Blonde and leggy, she had a gap-toothed smile that lent her an air of child-woman vulnerability.

Like a modern-day Helen of Troy, she was the muse who was loved and lost, wooed, won and lost again by two of the rock heroes of the time - George Harrison married her, and his best friend Eric Clapton stole her away. In the course of these romances, Boyd had so many rock anthems written to her - Something, Layla, Wonderful Tonight - that the wealth of tributes bordered on profligacy.

With musicians' machismo, Harrison and Clapton once engaged in an all-night duelling guitar session for her hand. When Clapton won, she re-immersed herself in a fresh round of wild London parties and hectic foreign tours, until his drug and drink addictions eclipsed everything else in his life - and the spell broke.

"I was a very shy person and, I suppose, easily manipulated," says Boyd now. "Of course, it's flattering to feel someone desperately wants you, but looking back, it's quite uncomfortable to realise that you were the object of desire. That's quite a passive thing to be."

In her early fifties, Boyd still has something of the Sixties rock chick about her: a tight, plunge-necked top reveals a plump embonpoint and her waist is Sindy-doll trim. Her skin may be crosshatched with the lines of age, but the kitten-blue eyes are wide and the gaze direct.

She sits gracefully erect on a cream sofa in the huge, glass-walled atelier living room of her west London flat. Her work in front of the camera as a model has long since been swapped for a career as a professional photographer, but she has also been heavily involved in drug rehabilitation charity work since 1991.

Along with Barbara Bach (wife of Ringo Starr) and Lucy Ferry (wife of Bryan Ferry) - both of whom have been treated for alcohol abuse - plus Jools Holland's lover, Christabel Durham, she is currently engaged in a fundraising drive to provide support for addicts. The latest project is a concert, featuring Holland and his Rhythm and Blues Orchestra, which takes place tomorrow.

It is clear that Boyd's interest goes beyond celebrity tokenism; once married to one of the most famous addicts of them all, she has a well of bittersweet personal experience from which to draw. "I've become involved in this because of people - friends - who have been in trouble as a result of alcohol and drug abuse," she acknowledges. "It's harrowing, totally harrowing, to watch."

Certainly, the stories she recounts, in her soft, cultured tones, highlight the destructive flipside of rock and roll hedonism. Like many others in her circle, Boyd sampled the booze, dope and cocaine but, unlike Clapton, she knew when to stop. Her account of his descent into heroin addiction quietly conveys the aghast impotence of a helpless bystander.

She met him in 1966, just after she and Harrison were married. By 1970, Clapton was making no secret of the fact that he was besotted by his friend's wife, nor of his anger at her refusal to leave her husband.

One day, he turned up at the home she shared with Harrison in Henley-on-Thames, Oxfordshire, and proceeded to deliver an ultimatum. Even now, nearly three decades on, it sends a shiver through her.

She recalls: "Eric showed me this packet of heroin and said: 'Either you come away with me or I will take this'. I was appalled. I grabbed at it and tried to throw it away, but he snatched it back. I turned him down - and, for four years, he became a drug addict."

The conclusion she draws might seem over-simplistic - even arrogant. But Boyd long ago ceased to feel flattered by any man's obsession with her.

"At first, I felt guilt. Then I felt anger because it was totally irrational of him to blame me for something he was probably going to do anyway; it was very selfish and destructive."

She stayed in touch with him, and the months that followed, she says, were "the most horrible, horrific time". Heroin, that most isolating of drugs, transformed Clapton into a virtual recluse who rarely saw anyone and seldom answered the telephone. However, in 1974, he was finally weaned off the drug through electro-acupuncture. Later that year, he persuaded Boyd to leave Harrison.

"In my naivety, I believed everything was all right," she says. "He wasn't taking heroin, which I thought was the main addiction for him. But, as it turned out, his drug of choice turned out to be alcohol."

Boyd, who had never been on the road with the Beatles, began joining Clapton on tour. It gradually dawned on her that the pattern of his evenings was invariably the same. "Eric would just completely pass out wherever he was sitting, whether it was on the sofa or the floor, because he was saturated with drink. The realisation hit me: 'This isn't fun. He's not having fun'."

Among his acquaintances, Clapton's drinking became a running joke, and they would start taking photographs of him where he lay, comatose. Boyd would attempt to shield him from the attention. Clapton, however, would deny he had a problem, and become abusive and belligerent with friends who criticised him.

But, amid the relentless excess, there were quieter times, too, spent in Surrey at Clapton's turn-of-the-century Italianate country house with its garden designed by Gertrude Jekyll. "I loved living in the country; that was the best time we had," says Boyd. "It was the most staggeringly romantic garden. There was a sadness in the house and garden, a kind of melancholy which was very Eric, in a way, and very creative."

The couple married in 1979 but, gradually, Clapton's drinking took its toll on both him and Boyd, who was constantly on the alert, watering down his drinks and fretting about his safety.

"One Christmas, I'd cooked lunch and most people had arrived and I couldn't find Eric," she recalls. "It was snowing outside, and I went out and called him, but I couldn't find him and became concerned. I just imagined him stumbling around in the garden. Anything could have happened."

The house and garden were combed, until finally Clapton was found slumped on top of a log pile in the basement. Boyd's efforts to make him seek help - together with those of his mother and managers - were resisted.

It was some time before Clapton faced the truth, and agreed to go to a treatment centre in the United States. The respite proved to be temporary.

"It was becoming very difficult," says Boyd. "You'd look for the part of the person you know and love, but it was hard to find. I think Eric was worried about his talent totally disappearing if he stopped drinking, which is a common idea among creative people."

In 1985, it emerged that he had had an affair with an Italian actress, Lori Del Santo, who bore him a son, Conor, in 1996. (Conor died in a tragic accident six years later.) Boyd was devastated at the news of the impending birth; she and Clapton had actively tried to have a family, and she had undergone IVF treatment twice. She felt she had little alternative but to leave.

"It was the most difficult thing I ever did in my life," she says. "I loved him deeply, but knowing that he was still seeing Conor's mother, I felt there was no role for me." She claims Clapton failed to understand why she was so hurt by the news, or why she felt compelled to leave. He expected her to share his joy. "Because he loved me, he believed I would be pleased and happy for him that he had a baby," she says. "It was as if I was his best friend; that he could tell me everything without realising how deeply painful this was for me."

Although he begged her to stay, and engineered a brief reconciliation, the couple split up for good. Boyd filed for divorce; at 42, she was on her own.

"It probably took me six years to get over it, with four years of psychotherapy," she says. "My self-esteem was unbelievably low, and I found it really hard to build up relationships because I had been used to difficult people. Anybody who was sweet and nice to me was no challenge."

While Clapton was seen with high-profile women, including Michelle Pfeiffer and Sheryl Crow, Boyd concentrated on building her career as a photographer. She had one short relationship before meeting her current companion, property developer Rod Weston, in 1991.

Today, Boyd's ties with the past are still in evidence; on her bookshelves, alongside many photographs of herself and Weston, stands a bronze cast of Clapton's hand fingering the neck of a guitar.

When Clapton's son fell to his death from a New York hotel window, she was there to support him in the grim aftermath. They talk on the phone occasionally and sometimes meet up; ironically, he, too, has become passionate about providing help for addicts. Wryly, she refers to Clapton's decision to spend more time on the drug rehab treatment centre he recently opened in Antigua as "his new obsession".

I ask what it was about her that captured men's hearts, but for all the distance the years have lent her, Boyd seems genuinely unable to pinpoint why she became the ultimate rock muse.

"Maybe it had more to do with them," she says, shrugging. "Perhaps Eric just wanted what George had. I don't know - I just think it's amazing we've come through it and we're all still alive."

From the March 17, 1999 edition of the Daily Telegraph.