I remember, many years ago, reading about women who'd had mastectomies after breast cancer, and had been sent home with little bags of sand that they'd been told to place in their bras. It devastated them that this was considered an adequate substitute for a breast. Happily, things are different now, and every effort is made to incorporate whatever breast reconstruction is possible as an integral part of breast cancer treatment.

However, delighted as I am that this is the way things are now, it wasn't what I chose for myself. I opted out of reconstruction after I'd had breast cancer. I'd had enough of hospitals, clinics and surgery. But it wasn't an easy decision. Perhaps, in the future, I will have it. But it won't be because it will help me feel more like a complete woman again.

Frankly, if my entire body was removed, and only my head remained, somehow attached to machines that kept me alive, I'd still feel entirely female, just as I felt as a child, before my breasts had developed, before I even knew I had a vagina or a womb.

I have a memory of when I was very young. I remember trying to persuade myself that perhaps little girls grew up to become men, and little boys grew up to become women. Even at that age, I knew it was impossible, that of course it didn't work that way.

I know, too, exactly what inspired that strange wish. My father had bought my mother a new iron for her birthday, and my mother had been really upset. She had told my dad how insulted she felt, how awful it was that he imagined that this was some sort of treat for her.

My dad was bamboozled. "But you said you needed a new one." She told him what it was like, being stuck at home, while he went out to work, seeing other people, being in the world. She told him she resented that even though she was at home all week, he still left her at home on a Saturday morning while he went to play golf. I thought that sounded miserable. I didn't want to grow up and get an iron for my birthday, instead of being able to saunter off to the golf course to swing one.

Luckily for me, feminism happened before my young adulthood, and I had many more choices than my mum did.

My childhood yearning to grow up a man was transitory, a response to adult descriptions of a gender role. It had no biological roots. As I say, I know in my head that I'm female. I need no breasts, no vagina, no fallopian tubes to tell me that. If, as an adult, I'd had difficulty becoming pregnant, and doctors had examined me to find my fallopian tubes were poorly developed, or not there at all, I'd be no less a woman. That happens sometimes. Nobody's perfect.

Yet the memory of that moment of misery, that brief encounter with the helplessness of feeling my gender destiny was wrong, yet inescapable, has stayed with me. If my wish for masculinity had not been a thought that faded, but a feeling that grew, well, that would have been terrible. My male mind would have been trapped in my female body, in some sort of hideous locked-in syndrome of gender. How strong would that feeling of incarceration in gender expectation have become as I underwent puberty? It doesn't bear thinking about.

Except that some people do have to think about it. They feel female in their heads, but their bodies tell the world they should be treated as male, and should behave like males (or vice versa). Failing to conform to this sets them apart in the eyes of others. Yet conforming to it sets them apart in their own heads. What a relief it would be to learn that this is a condition called gender dysphoria, and that they can be helped to live their life in a body that more closely matches the life in their mind.

The idea that your body tells your mind what gender you are and is always, infallibly right is ridiculous. It's the other way round. Your mind tells your body, because that, biologically, is what your mind is for. Most people's minds confirm to their bodies that they are the sex their mind thinks they are. But human minds are so complex that even the most learned among us don't really comprehend how they work. Too many people report, using similar language, that the gender characteristics of their bodies don't match the gender identity they feel in their heads for such a phenomenon to be capricious, misguided or delusional. It's also possible that in the fight between brain and body, no gender identity emerges victorious. Some people aren't even sure if they have any kind of strong gender identity at all. They're pretty androgynous, and that's how they have to proceed with life.

In the late 1980s, there was a schism among feminist activists whereby some radical feminists began excluding women whose female identity was anything other than entirely conventional. This exclusion has been controversial and small-minded from the outset. It continues to this day, even though it seems plain that the last thing needed by women who have suffered so much trauma to be accepted for what they are, is this fundamental and fundamentalist rejection. Likewise, it's not surprising that women whose identity is so hard-won are often intensely interested in the subject of gender politics.

Some people do not seem to see that gruelling gender-reassignment is undergone to make the bodies of women less male, or, in the less highly publicised process of female-to-male transition, the bodies of men less female. We are, as I say, who we feel we are in our heads. Trans women, like so many women who have had breast cancer, sometimes need the help of surgeons, because it is helpful for one's social body to support and confirm one's biological identity, not contradict it.

That's why it's so awful to talk of trans women as men who have been castrated. Such people are women who have had the biological misfortune to have been born with bodies that are out of kilter with the much more complex biology of their female minds. That too, is why the trans community prefers people not to talk of being biologically or born female as opposed to trans female. Trans people are biologically or born female, but with detail of the flesh that traduces their ability to be physically and socially accepted for what they are.

The saddest thing is that feminism is all about liberating people from rigid ideas about the immutability of gender, about not stopping people from being able to do things just because they are female. It certainly shouldn't be about telling people that they are not quite female enough to be awarded with a shining medal saying: "Oppressed".

It is hard, being a woman, less hard now, in the west, than it has ever been. Most feminists do see it's unbelievably hard being a woman who is driven and compelled to have her body rearranged before society will treat her as the woman she is. No one attempted to turn trans women away from the recent SlutWalks, for example, thank goodness.

If feminism is about anything, it's about helping others to feel as confident and supported as possible. The more difficult that is for a woman, the more she needs the help and understanding of other women who have the luxury of taking their bodily identity for granted as a perfectly comfortable match to the person their heads tell them they were born, biologically, to be.