Of course I wrote back to tell her that I was indeed Ivy Ferrari's daughter. I was happy to have made the connection - but so, it seemed, was she. I couldn't quite grasp it. Beatles were glamorous; my mum was a harassed woman with inky fingers, unruly hair and scruffy skirts who sweated over a typewriter all day. How could they compare?

In the past I might have been indifferent to the overwrought love lives of the fictional staff of Ryminster hospital, but now they seemed to take on a glamour of their own. George never wrote to me, and my mother never wrote to Mrs Harrison, but the two of us began a correspondence that lasted for several years - years that took her from the Mackets Lane council house to a smart bungalow in Appleton, George from gangling teenage guitarist to married man, and me from schoolgirl to young woman.

I sent Mrs Harrison signed copies of my mother's novels. She sent me signed pictures of the Beatles. I asked her intense questions ("Which one is your favourite, besides George?" Answer: "John, because he does the tango with me in the kitchen and makes me laugh"). She interrogated me about the mysteries of my mother's creations, such as whether my mum knew any real doctors like Dr David Callender. ("He was fairly tall and tough-looking, with tawny-brown hair and a lean, intent face. His eyes were dark and compelling, so full of fire and life they drew me like a magnet . . .")

On my 15th birthday, Mrs Harrison sent me a small piece of blue fabric, part of a suit George had worn at the Star Club in Hamburg. Once, I got a crumpled newspaper cutting containing a photo of the Beatles with their scribbled signatures on it, and a big lipstick kiss, which, she said, had been planted there by John Lennon.

She sent me notes that George wrote her on used envelopes: "Dear Mum, get me up at 3, love George". She wrote on the backs of old Christmas cards and odd bits of paper - I never knew why. She told me funny stories about her upbringing in Liverpool, a world of men in caps on bikes and old ladies with jugs of gin.

I told her about my life in Norfolk, about my sisters, my pony, the dog, my mother. I told her things I didn't tell anyone else - my fear of failure, my terrible, hidden shyness, my longing to have real adventures, lead a different kind of life to the quiet, rural existence I endured. She was my invisible friend, the silent recipient of everything I had to say.

She always answered my questions, and offered up teasing glimpses of life as the mother of a superstar - "I'm sitting by the pool with Pattie. Had a lovely time at the film premiere" - remarks tantalisingly combined with more mundane observations about knitting and cakes. Of course I never mentioned "real" boys who had caught my eye - that would have been somehow unfaithful to George. That was the only omission I can remember - apart from never articulating how I felt about her son, because I wanted her to think of me as a "normal" girl, and not the wide-eyed obsessive I really was.

After several years the gaps between our exchanges grew longer, as real life began to get in the way of teenage fantasies. I can't remember which of us wrote the last letter, but by the time I was 18 and working in London, the correspondence had petered out.

Soon after we had slipped from each other's lives, I found myself standing a few feet away from George himself, in the Apple boutique on London's Baker Street. He looked tired and unapproachable.

The George that I had conjured up in the kitchen of Mackets Lane, propping notes for his mum on the mantelpiece, seemed a kinder, gentler prospect than the gaunt-looking superstar standing before me who might just tell me to get lost. He was close enough to speak to, but I've never been sorry that I backed away in silence.

Mrs Harrison died in 1970 when I was 21. I remember reading about it in the papers. I grieved for her on my own, and remembered her small acts of kindness to a girl in Norfolk she had never met. Her son, of course, made an enormous mark on my life without ever knowing it. I even married someone who embodied all the things I thought George represented: quiet strength, spirituality, the same dry humour, the dark good looks.

My husband Colin had been, among other things, a roadie and the owner of punk record shops. Fortunately, he also had a sense of humour and a high level of tolerance. He learned to live with the omnipresence of George, and would sign cards to me "Love from George and The Other One".

As the years passed, my life came into focus and George receded. He married, had a son, as did I. I went back to live in a Norfolk cottage, while George retired to a Gothic mansion in Henley. In 1994 I went to Liverpool for the first time with Colin, as a football supporter rather than a Beatles pilgrim: Norwich City were playing at Anfield.

I took time out to stand in front of 174 Mackets Lane and tried to imagine Mrs Harrison sitting at the window in the front room, answering my letters. I wanted to weep, but I didn't. When Norwich scored the winning goal that afternoon and we leapt to our feet, I cheered instead for that kindly Liverpudlian who took the time and trouble to light up my teenage years.

I've gradually lost the priceless relics of those years. They would have made me rich if I hadn't been so careless with my belongings; then again, I would never have sold them. So my side of that eccentric correspondence has all but disappeared, along with my youth.

In September 2001, Colin died of Hodgkin's disease. A month later, George was dead, too. It felt as if two distinct parts of my life had ended all at once: my dreamlike girlhood, and my real, adult life with a beloved partner and friend.

But every day in my study at home, I look at something that binds these two parts together. It's a photograph of George taken in 1962 in Hamburg by Astrid Kirchherr (girlfriend of "fifth" Beatle Stuart Sutcliffe).

Colin secretly sought it out, hand-made a frame for it, and gave it to me on my 40th birthday. It is one of my most treasured possessions.

GUARDIAN