Where China leads, the world follows. A fifth of British couples now have one child only and the “Beanpole” family, (one single line as compared to the traditional 2.2 triangle) accounts for almost a third of all new families in America.

If it’s not a contradiction in terms to say so, the number of “only children” is exploding — so last month’s first ever conference in London to explore the phenomenon was a trifle overdue. It trotted through the downsides — sole responsibility for ageing parents and a tendency to be stereotyped as the spoilt, selfish one, while nodding to the positives: self reliance and independence, not to mention all that adult attention and cash lavished on one ’s formative years.

But what’s it really like to be an only child? Do the pluses outweigh the minuses? Definitely, says novelist and only child Terry Pratchett, in whose Discworld books the heroes are rarely encumbered by siblings. “In fiction,” he says, “only children are the interesting ones.”

And the same is true, he argues, in real life — provided your parents make sure you have other children to play with. He describes his 1950s childhood as idyllic, running around in a gaggle of kids in what appeared to be a neverending summer’s afternoon. He never questioned the lack of brothers and sisters and certainly never mourned it. The only impact, if any, it had on his life was that he got bigger presents than his mates because, although money was tight, it didn’t have so far to travel in his family.

A common brickbat flung at only children which came up time and time again at the London conference was a feeling of “otherness” — a feeling of alienation which steered one lone child into a career as a long-distance lorry driver — but it’s not something Pratchett ever experienced.

“The nice thing about being an only child is that you can be sociable or independent as the mood takes you,” he says. “You don’t have to break off what you are doing to look after younger brothers and sisters.” The only possible downside was, he says, the lack of muscle in the family. “I envied the kids who had big brothers because that meant they could beat up the kids who would beat you up.”

He bats away another commonly held belief that only children are selfish. “If you’re the only one, you have no-one to share things with, so it’s not the same,” he points out with infallible logic.

And far from feeling precocious or freakish, he says, being an only child may have helped provide him with the depth of knowledge he draws on to write his fiction.

“I developed a broader grasp of general knowledge because my mum had time to talk to me,” he says, adding he probably learnt more talking to her on the way to school than he did once he got there. It was she, he pointed out, apropos of nothing in particular, who named their tortoise Phidippides after the Greek hero who ran from Athens to Sparta.

But where has this sudden rash of only children actually come from? Jenny Eclair, comedian, writer and the mother of an “only”, blames the parents, especially the mums. “It’s because we are selfish as a generation,” she says. “We can’t compromise. We don’t do sacrifice any more. We want children and we want a new pair of shoes as well, and the only way to do both is to have one child.”

She’s only half joking. “I live in southeast London, which means I have paid for my daughter’s education since she was two,” she says. “We couldn’t have afforded to do that for two children.”

Eclair’s daughter, Phoebe, is now 16. During Phoebe’s early years her father, Geoff, was busy working 9 to 5 while her mum was building her career as a stand-up. “He would come in after a day’s work and I would throw the baby at him as I headed out to some grim pub,” says Eclair.

“I found the baby years very difficult — it was quite traumatic,” she says, adding that it was only when Phoebe was about nine that she began to have anything approaching regret for not having had more. She attacks the myth of happy family life in her new novel, Having a Lovely Time, but says she envies what she describes as the smug supermums with five children and their cosy, chaotic crowded sofas.

But there are pluses: being an only child has led to her daughter growing up to be both focused and conscientious. “She always sees something through to the end,” says Eclair, which is why this year it is Phoebe who is performing at the Edinburgh Fringe festival rather than her mother.

“I do have a theory that only children’s characters are undiluted. In a positive way that means she doesn’t have any siblings to either knock the edges off her or to sway her from her path.”

Comparing it to her own childhood, as the middle child between an elder sister and a younger brother, Eclair says: “I had a very academic, very good, older sister, so I felt duty bound to be the opposite.” To this day she credits that for making her “the big loudmouth showoff I am today”.

Parents of only children can take comfort not only from Eclair’s observations but also the roll call of illustrious onlies, which takes in Frank Sinatra, Charlotte Church and Tiger Woods. But perhaps the most reassuring words are Pratchett’s: “I genuinely never had a brother or sister-shaped hole in my life.”

Additional reporting by Deepa Shah