It's tough if you don't want kids. Not only must you put up with your parents hounding you about grandchildren, these days the Government has joined in as well with its high-profile support of families with children. Then there is the general assumption about the childless that they must have fertility problems (prompting unwanted pity), or that they are selfish (arousing disdain) or that they will change their minds (prompting endless interference and wise counsel).

Yet surprising numbers of couples are absolutely determined not to have children. A recent report revealed that one in five of all British women born in 1975 have set their minds firmly against motherhood. So it is hardly surprising that Britain's birth-rate - which currently stands at 1.7 children per woman - is at its lowest level in 150 years.

Many of these women (no one asked men about wanting to be fathers) feel that they have very good reasons for their choice to be childless. But they would rather not spend time explaining themselves. Indeed, they have become so fed up with the attitudes of others that some have even joined a campaigning organisation - the British Association of Non-Parents.

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The association aims to puncture many of the myths about chosen childlessness. The first is, of course, that women alone choose not to reproduce. The chair of the BANP is Root Cartwright, a non-father.

"I'm nearly 49," he says. "I have been thinking about this issue probably since I was in my late teens. I have never wanted to be a father. I have never wanted that sort of responsibility. It is the fact that child-rearing goes on every bloody day for so long. Many will say that I am a feckless, irresponsible person or just a miserable, po-faced old sod. But I'm neither. I just do not want to devote myself in this way to children.

"I had a vasectomy 15 years ago. It was extremely liberating. It was a way of saying definitely this is how I feel. I have never experienced any regrets." Mr Cartwright, an artist, was single at the time, but for the past 11 years has been in partnership with a woman, now aged 46, who likewise has decided against having children.

Jayne Sutcliffe, 31, a civil servant from Barnsley, is used to being questioned constantly about her decision, jointly taken with her husband Paul Marshall, 36, a software development engineer. She is not a high- flying yuppie, the stereotype of the career-minded woman, who has no time for children. As she says herself, she is not particularly ambitious. All of which makes her decision even harder for others to understand.

"People say to me: `You're 31. Are you thinking of having children?'. `No, we're not,' I answer. `Why not? You would be wonderful parents,' they say. And so it goes on. I have cats. They are great but I wouldn't say that everyone should have one, so why do people automatically think that I should have children?

"At first my mother thought there was some kind of medical problem that I had not told her about. I explained that I just did not want them. But she still has not quite got the hang of the idea. She introduces me as Jayne, the one who doesn't like children.

"That is not true. It's not that I don't like children. It's just that I don't want any of my own."

Ms Sutcliffe argues, like many childless adults, that they are in fact more alert to the needs of children than are many parents. "I'm not really blessed with abundant patience. Yet that is something you need in bucketloads if you want to have children.

"I also think it is terribly unfair to accuse people like me of being selfish. Surely it is more selfish when people have children because of what they hope the child will do for them, rather than what they can do for the child. It would be selfish for me to have a child because that child would grow up with a parent that did not really want him."

Ms Sutcliffe and her husband have always agreed, she says, not to have children and, like other couples who choose childlessness, that agreement seems to be central to their relationship. "I would not compromise on having a child," she says. "We have been married for 11 years and Paul had a vasectomy three years ago. It was such a relief. When you have not taken any steps like that and people find out you don't want children, they say that you still have time to change your mind. But once you take a radical step, they stop saying things like that."

Jane Elliot finds British attitudes towards those who choose childlessness very odd. "The British seem to think that there is something unnatural about it. I don't understand why it is such a big deal here," says Ms Elliot, an American, who teaches people with impaired eyesight how to regain their independence. Ms Elliot, 42, lives in Brighton with her husband Chris, a 43-year-old electrical engineer. She adds: "I have simply never been interested in raising children. In my twenties I lived in Japan and in my thirties I travelled overseas a lot, working in marketing. So I had an exciting life, although that is not why I did not want children.

"When I came to England I went to a GP and told him I did not want to use the Pill. I asked for an IUD and told him I did not want children. The GP refused to believe me, would not give me an IUD and said he wanted to talk to my husband. It was so sexist."

For Ms Elliot, like many others, her initial decision not to have children has been constantly reviewed. "I have gone through a period as I have approached the end of my fertile life when I have wondered whether I made the wrong decision. But after a lot of thought, I have come to the same conclusion. Now I'm 42 I don't think I am going to change my mind."

Lysette Butler, 38, from Morden in Essex, likewise re-examined her decision when, three years ago, she chose to have a hysterectomy sooner than her medical condition made strictly necessary. "After I had the hysterectomy, lots of people were wondering whether I would have regrets. So I waited for all these feelings. They never came. In three years, there has never been a day when I have thought, `God, what have I done?'"

Mrs Butler, who manages the gynaecology unit of an NHS hospital, has been married for 14 years to Barry, a retail manager. Like other couples, they protest that they had normal, happy childhoods, that they like children, but that they also enjoy handing them back when they have been babysitting. She says that society is becoming more tolerant of childlessness, but still some people feel hounded.

"People should leave us to make our own choices. No one else has to live with our choice. I think we should have the right to ask people why they want children and expect them to have proper answers. I suspect a lot of people do not have a good reason."