“I currently rent a flat on the top floor of a house owned by a friend,’ says Anneka Sutcliffe, 33, a well-educated professional violinist from Bristol. “I’m not currently in a relationship but I have had various partners, some of whom I’ve broken up with because of the issue of having children – they wanted them, I didn’t.” She would consider adoption, she says, if she had a stable home and suitable partner, “but adding an extra human to the planet is about the most polluting thing you can do.

“It would be too heartbreaking to love a child so much and see them trying to deal with the problems we have created in the world.”

‘Climate anxiety’ and fears about the damage created to the planet by human activity seem manifest among educated young people. Caroline Hickman, a psychotherapist from Bath University, is co-author of an international study published last month in the Lancet Planetary Health Journal. It surveyed 10,000 16 to 25 year-olds between April and July last year in ten countries across the world including Britain, France and the USA. More than eight out of ten were worried about climate change and 75 per cent about their own future.

“We asked them specifically whether they felt cautious about having children and they did,” Ms Hickman said. “If young people don’t see the future as having positive outcomes for them, they aren’t going to have children.”

Some embracing this viewpoint have accepted real sacrifice. Tim Jones, an experienced 38 year-old teacher, gave up a successful career in a major London school to become a full-time climate campaigner, living with his 30 year-old girlfriend on a canal barge in Oxford.

“I would love to have children, I come from a big family but I’m also terrified about what that means,” he says. “Every human that’s born, especially in a rich country like ours, has a huge impact [on the planet] just by living… I felt we shouldn’t be preparing children to pass exams, we should be preparing them to learn how to survive in the world that’s coming.” Jones says his own parents are supportive of his views – his brother and sister have already provided grandchildren. His girlfriend is more ambivalent.

Two retired doctors interviewed for this report said they had given their daughters funds for egg-freezing and tests to check egg reserve, but neither had dared to inquire if the money had been used.

“My daughter is 33 and my wife and I still hope she will find the right man and settle down, even though she’s not showing any interest in doing so,” said one. The daughter of the other doctor is already 41. “She just seems to have chosen men who aren’t interested in committing to a relationship, and says she doesn’t want to bring a child into such a precarious world anyway,” he said, sadly.

Some psychologists point to the growing phenomenon of “delayed adulthood,” particularly among younger generations of men. They postpone “not just sexual activity but also other activities related to mating and reproduction, including dating, living with a partner, pregnancy, and birth,” says psychologist Jean Twenge from the University of San Diego.

She points out that this behaviour is part of a broader cultural trend where modern teenagers are less likely to drive, drink alcohol, go out without their parents, and have paid jobs. Sexual inactivity is related to joblessness and economic dependence on parents.

Elsewhere in the world, birth rate decline has fuelled fear of reliance on immigrant labour. Poland and Hungary are restricting access to abortion and contraception with the suggestion that selfish women are to blame for the collapse of white Christian civilisation.

“We want Hungarian children. Migration for us is surrender,” declared Viktor Orbán, the Hungarian prime minister, who has devoted around five per cent of GDP to boosting the birth rate. Married couples can apply for free IVF or a loan of about £25,000, which they don’t have to repay if they have at least three children.

There is little evidence for the success of any of these incentives; nor have Scandinavia’s generous policies of extended parental leave and subsidised childcare – often hailed as the gold standard by “liberal pronatalists” campaigning for similar encouragement for couples here – halted their own falling birth rate.

A 2015 poster campaign in Denmark asking women if they had counted their eggs today was condemned for likening women to farm animals. Soren Ziebe, head of fertility at Copenhagen University Hospital, who was involved in the campaign, remains unrepentant.

He considers much of the decline in birth rate – currently 1.7 per woman in Denmark – is due to reproductive ignorance.

“We are brought up with sex education at school and the assumption that unless you use contraception the woman will immediately get pregnant,” he says. “Humans are actually not very fertile. There’s only a one in three chance of pregnancy per cycle for a woman in her 20s when she should be at peak fertility. The average age of first birth for mothers here is 29.5 when the chance [of conceiving] per cycle is only 17 per cent. It’s very important men also know this.”

And he lays some of the blame, closer to home. “As prospective grandparents we give our children poor advice – get an education, travel, focus on your career – we push them in directions where they are less likely to have children.

“When we ask school children if they want kids almost all of them do, but people have grown up with the assumption they can decide when to have them. You have to find a partner and a place to live. Our biological clocks don’t care whether you have finished your education or found a job.”

Indeed the rise of “workism” – one’s career is the cornerstone of identity – often seems to mean that work-life balance simply equals more work and less family for many people; and for women, may mean no family at all.

“No one’s lain on their deathbed and wished they had fewer children,” claimed the television presenter Kirsty Allsopp, who was famously attacked for declaring she would tell a daughter to have a child first and start her career later.

Dorothy Byrne, the incoming president of Murray Edwards College in Cambridge, previously head of news and current affairs at Channel 4, drew similar outrage at her “patronising” decision to introduce fertility education to women students this term. This was born of her own experience of difficulties in conceiving: “I wish I’d been told, for example, that if I’d started trying just two or three years earlier, I could have doubled my chances of success,” she said. “In the end, I had a baby when I was nearly 45. I think more information is always a good thing.”

Others argue that more information shows remaining childless is a sensible choice. “The healthiest and happiest population subgroup are women who never married or had children,” says Paul Dolan, professor of behavioural science at the London School of Economics and author of Happy Ever After, which compared levels of pleasure and misery in unmarried, married, divorced, separated and widowed people.

Alistair Currie, spokesman for Population Matters, a charity campaigning to raise awareness of global overpopulation, unsurprisingly also sounds a note of optimism: “I think falling birthrate will be very positive in Britain,” he says. “We are one of the most densely populated countries in Europe, seriously depleted of natural resources and landscapes – pollution levels are very high. Having fewer people doesn’t solve these problems but it does take the pressure off.

Whatever happens, he points out, there will be an extra three billion people on the planet by the end of the century and gaps in the labour market may be addressed by automation, immigration and incentivising healthy older people to stay in the workforce beyond retirement age.

While many fear the social upheaval of this impending grey revolution, “there’s a real risk of people not seeing these trends for the benefits they are,” says Currie, who himself has an 11 year-old son. “People should definitely not be too frightened to bring children into the world at all.”