There are countless writing rules that authors are urged to follow, but they can probably all be boiled down to one: seize your reader’s attention and keep it. Phoebe Smith, one of the most popular writers you’ve probably never heard of, has to consciously ignore this when the muse takes her.

“I kind of flip over what we would normally do with writing. We’re normally trying to grab people with a dramatic introduction, and work through a narrative arc with every paragraph we write,” she says. “I’m flipping that on its head.”

Smith was a travel writer and journalist when she was approached last year by Michael Acton Smith, co-founder of the sleep app Calm. She’d written an article about the Trans-Siberian Railway and he asked her if she’d like to rewrite it for him, “as a story to send people to sleep”. She was nonplussed – “I thought, ‘Should I be really offended that he thinks my writing has the effect of boring people to sleep?’” – but decided to give it a try.

A year on, she has written 15 pieces for Calm, whose catalogue of “sleep stories” has been listened to 100m times. Running around 20 to 40 minutes long, Smith’s stories draw on her travels, from the wilds of Morocco to her train ride across Siberia, following wild ponies in Virginia or trekking through pristine forests in Sweden. Her most popular, Blue Gold, has been listened to around 15m times: read in the mellifluous tones of Stephen Fry, it is a gentle, soothing tour around the lavender fields and sleepy villages of Provence. She’s also written the Joanna Lumley-narrated Elephants of Nepal, which follows a safari across Chitwan National Park.

Smith has now been given the rather pleasing job title of the “world’s first sleep storyteller-in-residence” by Calm.

“With most kinds of writing I’m trying to build the tension – here, I’m doing the opposite. Anything exciting needs to go right at the beginning and then it’s all about winding people down, while also encouraging their imagination to play,” she says.

With recent research by the Sleep Council finding that 27% of Britons sleep poorly on a regular basis, and a 2016 YouGov survey showing that 46% of British women and 36% of men report trouble sleeping, it seems we need all the help we can get. A bedtime story requires just enough focus to distract from emails and other workaday stresses to help quiet the mind – but it can’t be too exciting, either.

Smith describes her stories as “toeing that line of being interesting enough they want to hear it and slow and steady enough that they never actually hear it all”.

She is careful with her word choices, avoiding any disruptive sounds that might cause someone to wake up. There’s lots of immersive description, lots of onomatopoeia, lots of soothing, sonorous language. “You’ll smell it before you even see it, that unmistakable aroma that fills your nose and seeps into your senses, instantly mellowing into a smooth and soothing scent,” intones Fry, as Blue Gold opens.

“We’re so busy and so connected to everything we just don’t allow ourselves that time any more to unwind before we go to bed,” says Smith. “It goes back to when we were children and would have someone read to us to get us to go to sleep. I don’t know why we ever give that up; that always worked then, why wouldn’t it work just because I’m a grown up?”

Most of Calm’s sleep stories are fiction, but Smith specialises in travel-related non-fiction. She’s set to go on a “sleep story tour” of the UK and Ireland next month, and is wondering what effect she’s going to have on her audience. “I hope people will doze off, it will really be a book tour with a difference. Normally I would be mortified if anyone went to sleep. This time, I wonder how many people I can get to nod off,” she says. “People say to me, ‘I really enjoy the stories but I never get to the end!’”