WE ONCE had a fight, I remember, over who pushed the trolley in Sainsbury's. I suppose I was about eight, which would have made him between six and seven. I can still hear the hard adult voice, remonstrating: 'What a selfish girl you are - think of all the things you can do and he can't] Let your brother push the trolley]'

This is not an argument that an eight-year-old understands, but I believe it has the power to inculcate the kind of guilt that settles on the psyche like superglue. Twenty-four years later, at 32, I've only just begun to chip away at it.

Let me tell you another story. When I was 15 my best friend stayed the night at our house after a party. In the way younger brothers do, mine came into our bedroom at some brutally early hour and stood at the foot of my friend's bed, chattering. 'Piss off, Matty,' came the voice from under the duvet. This is my happiest adolescent memory: she was treating him like anyone else's little brother. It made me feel normal, and God that felt good.

Mathew was probably born with a fully operational brain, but it was damaged when he was a baby. My parents never found out how: it could have been the result of a whooping cough vaccination at nine months, or complications during his very swift birth, or some kind of fever.

In the Sixties healthy kids weren't allowed into children's wards. With my outdoor coat still buttoned up, I used to press my nose against a big glass door stencilled with long words in green paint. By the time he was five the family were so weary of hospitals and tests that the search was laid to rest and Matty freed from his torturers.

Mathew's intellectual development was slow; slower than most children in learning how to wash, dress and look after himself; at the age of seven he still needed the attention normally accorded to a three-year-old. Day-to- day activities took longer than they should have. He was also hyperactive and emotionally volatile.

Mathew absorbed a disproportionate amount of our mother's time. I was generally left, not disagreeably, alone with my book and Fuzzy-Felt while Mathew was prepared for an expedition into the threatening world outside our flat. From an early stage it was taken for granted that I was quite capable of tackling whatever task was at hand. After all, compared to him, I was all right.

I honestly do not remember resenting him, however much I search my heart. But I really must have.

What I want to say is this. As the sibling of a handicapped child you are likely to feel resentment, dislike and even hatred, and you will probably feel guilty about doing so. I think the psyche turns this morass of pain into something quite other, so that it is no longer recognisable. Then, like me, you don't remember the shameful feelings. Into adulthood I marched, carrying heavy emotional baggage I couldn't unpack.

When I was at primary school, having friends home was a nightmare. Mathew always wanted to come into my room and join in. I was ashamed that he was 'different' and didn't want him there; my little friends couldn't cope with his odd behaviour.

Mathew's frequent migraines were another embarrassment. They often occurred half-way through a special occasion, such as a birthday party; they usually involved turning all the lights out (to ease the pain) and clearing vomit off the carpet. I still have difficulty coping when happy occasions come to an end: I got stuck in a pattern of them ending badly.

I was always highly motivated. Nobody in our street could believe it when I got straight As and an exhibition to Oxford. This commitment was a gift from Mathew. But somewhere in my subconscious I had to allow myself to be weak, and in that murk I floundered. An eating disorder was one manifestation of my efforts to satisfy unmet childhood needs.

Mathew lurched from special school to special school before settling at a Steiner place we all liked. He didn't board until his mid-teens. I can't actually remember much about those years, which is probably significant in itself. I do know that in the holidays, we always had to head for places where everyone else wasn't: the empty cafe, the deserted corner of the park, the holidays in camper vans.

Mathew is physically perfect: six feet tall and very handsome, with dark hair, dark eyes, and a muscular and slim body. He celebrated his 30th birthday last year, lives in a converted stately home run by an independent trust (his local authority pays) and works on a farm for the intellectually handicapped. He has just done a sponsored walk and raised pounds 100 towards a minibus for handicapped children in Romania. He cannot read or write, or go out alone, or use money or the telephone. He knows how to enjoy himself, and is tremendous fun to be with. Although he can still be unpredictable, his behaviour is not as erratic as it was when he was 25, when he was still likely to lie down in the supermarket or hit our mother in public.

He often says directly what the rest of us conceal. At my home recently he met, after 10 years, a girlfriend of mine whom he had seen frequently throughout our teenage years. 'Lyn]' he cried immediately and joyfully. 'Do you like me?'

I can put my hand on my heart and say that I feel lucky to have him. I don't feel guilty about wishing there had been more of us; I think other brothers or sisters would have helped me. I feel angry that nobody ever explained anything to me or acknowledged that as 'the other child' I had special needs, too. I didn't hear the phrase 'the handicapped family' until I was 29: it hit me like a ton of bricks. We had a name] Earlier this year I discovered that Mencap runs a sibling support service for adults. I was pitifully thrilled someone had recognised that a childhood like mine does have implications for adulthood.

I feel happy with the way my life is turning out: I love my work as a travel writer very much. But I am frightened of intimate relationships, a difficulty that may be connected to my childhood, and I wonder if it is any coincidence that I am still single.

The important thing for the adult with a handicapped brother or sister is to recognise the burden of resentment and pain, and work at freeing yourself of it. I was amazed at how much this (very lengthy) process helped me to understand myself. I hope that siblings who are children today do not have to drag that confused and needy inner child into adulthood.

(Photograph omitted)