"The only thing that will fix these problems is to have fewer people on the planet. I don't see it's justified to make more people than we already have. Yes, I have a maternal instinct, but I will never change my mind."
Drastic? Perhaps. But, astonishing as it sounds, Oonagh is one of a number of British women who are deciding to remain child-free, not because of career aspirations or an inability to find a partner, but because they are concerned about the crippling impact of overpopulation on the Earth.
Crazy? They would urge you to consider the facts. The global population, they say, is growing at a rate of one billion every 12 to 15 years.
By the year 2050, it is estimated it will have grown by 30 per cent.
While much of the population explosion is happening in developing countries where lack of contraception and education means women have more children, the issue is just as pressing here in the UK.
Their proof? Last year, the UK's population saw its sharpest annual increase in nearly 70 years.
Although the Office for National Statistics said that net international migration was the main driver behind the growth, there were also rises in births and fewer deaths. With our heavy consumption of fossil fuels such as petrol, coal and gas, they argue, we currently use nearly three times the renewable resources our land can provide.
We're also one of the most nature depleted countries in Europe, losing species of wildlife at above the global average rate.
In addition, we're reminded, we need 200,000 new houses a year to meet the demands of our growing population and, astonishingly, the densely populated south-east of England ranks 161st out of 180 areas globally in terms of its ability to deliver sufficient water to its inhabitants.
"You could say I'm selfless by not having kids, as I'm not contributing to overpopulation. This makes it easier for you and your kids to get a place at school," she says. Anna, a cycling instructor, was brought up to be 'respectful of the environment' and realised in her early 20s that despite being one of four sisters with two nieces and three nephews, she wouldn't have children herself.
"We are using more resources than the earth can provide and we cannot continue to expand exponentially — it's simple maths," says Anna, a vegan who buys clothes from charity shops and lives in a houseboat on a canal in Bath, Somerset, to help limit her own eco-footprint.
When she first told friends of her decision, they all assumed that she'd change her mind eventually — a response she finds patronising.
"Here I am in my mid-30s and I still haven't changed my mind.
"Most of my friends now applaud me for sticking my neck out. Some ask if I feel critical of them for having children, but they understand my reasons."
Anna has only had one relationship in which her decision not to have children caused a problem.
This was with a man she dated for two years in her mid-20s who believed she would eventually agree to have a child. "I didn't, and we broke up," she says. Now single, she'd love to settle down and feels hopeful that her refusal to become a mother is a bonus.
"Nowadays, most men I meet are on their second marriage and already have children. So I don't think not wanting them would be an issue.
"It would be lovely to help bring someone up. But they don't have to be my own flesh and blood."
Part of her reasoning for not becoming a mum is that she fears for what kind of future her children would have, should the effects of overpopulation continue.
"I will be gone before this has a real impact, but I worry about my nieces and nephews. What will their future be like? It's terrifying."
Certainly, she has cause for concern. Because of our rapidly growing population, an extra 750,000 school places will be needed in England by 2025.
And, according to the United Nations, with 410 people per square kilometre, England is already the most overcrowded large nation in the EU.
For Helen Campbell, 40, from Hay-on-Wye, South Wales, the decision not to have children is linked to her desire to counteract her less environmentally-friendly activities.
"My husband Kenny and I love sports cars, we enjoy flying on holiday and live in a big listed building that doesn't allow double glazing. This adds to our fuel consumption," says Helen, who owns a company that makes mugs with local artists. "There has to be a balance. We can't all do everything we want and it's about what I can do to lessen my impact.
"Humans are bad for the environment and I don't like the idea of being responsible for putting another one on the planet."
She says she had already made up her mind by the time she met Kenny, 50, a reporter for Formula 1 racing, in her mid-30s.
"Friends and family thought I'd eventually feel this overwhelming urge to reproduce but I never have," she says.
She admits to encountering hostility over her views. "I met a woman at a concert who said she 'used to be selfish' like me before she had her son.
"Another woman I worked with once burst into tears when I said I'd never have children because she couldn't fall pregnant and couldn't believe my choice.
"But I don't think what I'm doing is bad."
Kenny, she says, is similarly reluctant to have children.
"For me, the environment is a bigger issue whereas for him his demanding job would make parenting impossible," she says.
Cambridge University graduates Joe Gray and his wife Romita, both 36, who met as students and married in 2007, are also adamant they will remain child-free.
Joe, 36, a medical editor from St Albans, Hertfordshire, says the harm humans have on animal species is the driving factor in his decision.
"I don't want to add to the species — every additional child is another person to consume resources and take up more of the dwindling space that remains for wild nature. I'm not anti-human, but it is ethically wrong to drive another species to extinction."
His wife Romita, 36, a health economist and natural sciences graduate, is also concerned about the impact of overpopulation on humans. She admits that her mother was a 'little bit disappointed' by her decision not to have children, and that, as she reached 30, she wondered whether she should reconsider.
But, she says, after a few months, she knew she'd made the right choice. "I'd feel so guilty bringing another child into the world, who would use up constrained resources. It wouldn't feel like a positive move."
Yet Joe admits he has faced opposition. 'When people ask me why I'm not having children I tell them. People don't want to take the issue seriously, and my view gets caricatured as if I'm some sort of crackpot who wants humans to die out.
"In fact, taking overpopulation seriously before it's too late offers the key to humans having a long-term future."
And, the United Nations argues, if every family had an average of half a child less in the future than currently predicted, there will be one billion fewer humans than it expects by 2050, and four billion fewer by the end of the century.
"We need to think about the impact that extra child has on friends, family and neighbours, the wider community and the world," says Maynard.
"It will take time, but if we persuaded people to stop at one or two children we could start moving towards a sustainable population."
Are you a parent in New Zealand? We want to hear from you. Join our parenting group on Facebook.
