WHEN Esther Rutter announced she was knitting a swimsuit, her family was sceptical. Won't it itch, wondered her mother-in-law. Might it sag and droop, worried Rutter herself, as she cast on in with soft, washable, Scottish Borders yarn.

But Rutter, who was researching the history of British wool-work, was determined to see it through. Scotland's southern mills had once been renowned for producing the knitted swimwear that would revolutionise early 20th-century water-sports. What's more, Rutter had heard intriguing tales from people who'd grown up in the 1950s and 1960s about the excruciatingly uncomfortable woollen swimsuits their grannies had made them. "I just thought – this is clearly a cultural experience I've missed out on by being born in the 1980s, so I'm going to give it a go," she says. "I knew that the itsy bitsy teeny weenie yellow polka-dot bikini was the world's most iconic swimming costume, so when I found an old pattern I decided to make one and it turned out better than expected."

Rutter tells me this as we walk to the Pittenweem beach, where she's offered to demonstrate the finished costume's aquatic suitability. The verdict, she reports, is that the bikini is neither saggy, droopy nor itchy. Instead, it works rather like a wetsuit, growing progressively damper as water soaks the fabric.

"Wool can hold up to 35% of its own weight in water before it stops being insulating," she says later as we chat in the cosy surroundings of Pittenweem's Woolly Brew yarn shop. This astounding quality, she continues, was discovered by Mount Everest Expedition physiologist Griffith Pugh. "He found that wet clothes which are made of synthetic or cotton fabrics almost make you colder than if you were naked, so if you get caught in a storm while wearing synthetic or cotton materials you will die of cold, because it just can't create the warmth. Whereas wool remains insulating even when wet."

Rutter is full of fascinating facts about this most natural of materials. The Fife-based author has, after all, spent a year travelling from Shetland to the Channel Islands, unravelling the history of woollen crafts for her new book, This Golden Fleece: A Journey Through Britain's Knitted History.

Having lived on a sheep farm and been a knitter since childhood, she'd searched for an entertaining book on the subject but found there was very little out there. "The thing about textile history," she says, "is that it's chronically under-researched because it's seen very much as 'a woman's thing'. It's also quite ephemeral, because natural fibres degrade over time. And because traditionally academia is the preserve of men and the domestic sphere is the preserve of women, there's not a huge amount of overlap between the two."

What Rutter wanted wasn't "a dry, technical history" but a book that would take her on a journey. Unhappy with her job in academic fundraising but with an English degree behind her, she began to think she herself might be the person to "unpick this hidden woman's world" and create the book she was looking for. A theoretical exploration of traditional woollen crafts would not, however, be enough. "I realised that in order to fully understand the stories of all those people who made these items, I needed to know how they made them – and that involved making them myself," she says.

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So in January 2017, she entered XpoNorth's Scottish Writers' Tweet Pitch, which invites would-be authors to tweet their book idea to literary agents in 140 characters. Her pitch – to knit her way around the British Isles – was picked up immediately and a book deal with Granta followed.

She also secured Creative Scotland research funding, which let her travel around the country, lodging in bothies and uncovering fascinating stories about the people who for centuries had spun, woven and knitted the clothes on their families' backs.

In Shetland, where sheep had grazed for at least 5,000 years, she tried intricate Fair Isle knitting. In Wales – which has three times as many sheep as humans – she made a traditional Monmouth cap. In Edinburgh, she created a "pussy hat" to be worn at an anti-Trump demo, in the process, uncovering the surprising links between knitting and protest. (Madame Defarge, who surreptitiously stitches the Revolutionaries' guillotine register into her knitting in Dickens's A Tale Of Two Cities, is perhaps the craft's most famous subversive but to this day, "yarn-bombers" continue to use woollies as a colourful form of graffiti.)

One of the most captivating stories to emerge from Rutter's knitting journey is rooted right here in the East Neuk of Fife, among the fishing communities who eked their living from the perilous waters of the North Sea. Specifically, it concerns the women who knitted the jumpers, or navy-blue "ganseys", that kept their husbands and sons warm and dry. "Heavy and dense, these traditional fishermen's jerseys are tightly knitted to repel water, encasing the wearer in a woolly cocoon," writes Rutter, adding that "ganseys were the de facto uniform of Britain's fishing fleet from the early 10th century until after the advent of waterproof PVC in 1913".

Rutter's account of the the history of the Scottish fishing industry – which employed a huge number of Scots following the Highland Clearances – is enthralling but the insight into the work done by those left on shore, which she researched with the help of the Scottish Fisheries Museum in Anstruther, is particularly illuminating. Women of these parts, she tells us, did not sit "haund idle". If they weren't baiting lines, gutting fish, barking nets or caring for their families, they were busy creating these intricately textured garments.

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The fact knitting was often fitted in around other things may explain why it's long been undervalued, suggests Rutter, though as she points out, even if basic garter stitch can be mastered by anyone, advanced techniques are complex and highly skilled.

The gansey is a case in point. Although created in a single colour, its construction involves creating elaborate and intricate textural patterns, which are said to have varied from port to port, fleet to fleet and even family to family. According to popular legend, each east coast village had its own distinct design and each individual jumper was unique so that a drowned fisherman could be identified by his knitted shroud, should his body be found far from home.

"It's a really good story," says Rutter, before adding that despite travelling the length of that coast, via Musselburgh, Whitby and even across to Guernsey, where a similar tradition persists, she found no evidence to back up the theory and learned that the bodies of drowned fishermen were rarely recovered.

All the same, she says: "I think we like the idea that there are little mysteries out there to be solved, and that you can use knitting to identify a person. And in Cornwall, I did find a record of a woman who picked out her grandson's jumper in a crowd, on the body of the thief who'd stolen it, because she'd worked his initials into it. So there is a grain of truth in the story."

Taking around 100 hours, often in the smoky darkness of an unlit cottage, the crafting of a single gansey was a mammoth task but Rutter, true to her hands-on mission, determined to knit one herself and the book charts her year-long odyssey of turning a kilo of fine, 5-ply wool into a sweater for her father who, as a gardener, is "the only person I know who works outdoors every day" and would therefore appreciate its unique, wind and rain-proof qualities.

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Crafting the garment was a peculiarly intimate process. Traditional ganseys, explains Rutter, were made "to fit the men who wore them, mirroring the bend of their back and the swell of their stomach" and running a tape measure across her father's torso brought her the closest she'd been to him since childhood. "This level of intimacy is almost unknown in our world of pret-a-porter and off the peg," she points out.

Nor have we always been comfortable with the notion of custom-made, hand-crafted clothing. For while people knitted and sewed for their families throughout most of human history, this changed when machine-made knitwear became readily available in shops and by the 1960s and 1970s, wearing a cardigan that your mammy had knitted was often a source of embarrassment. "There's been a very interesting change in people's attitudes towards fashion generally but specifically knitting," agrees Rutter. "Back then, being able to buy off-the-peg clothes was a sign of affluence. You would only have hand-knits if you couldn't afford machine knits, so hand-made woollens become a sort of shorthand for poverty."

Such was the stigma, in fact, that women sometimes removed labels from worn-out shop-bought garments and sewed them into their hand-knits. However, where once, yarn was cheap and finished garments were expensive, the situation has now reversed and today, textiles are experiencing their version of the real food movement thanks to the reaction against fast fashion and disposable clothing. "People want to be able to trace where their garments come from and identify the provenance of the yarn," says Rutter. "They value the time that's been put into making them. And because we've got loads of really innovative designers making really attractive patterns, knitting has been released from this idea of grandma sitting with her needles in front of the fire and it's actually quite trendy."

It's also, she says, a great leveller. "As long as you can afford two roughly equal bits of wood and a ball of wool you can knit. Everyone can access it and in a world where we now feel we are becoming less connected to people and the distance between us is opening up, it's a fantastic way of saying, one person to another – I love you, I care about you, I want to literally wrap you in my time and attention."

Never more so, than when a new baby is on the way. The Woolly Brew's owner, Fiona Wright, first took up the needles when her best friend was expecting and many of her customers are stalled knitters who've come back to the craft when they are about to become grandparents. Rutter herself discovered she was pregnant 10 months into her knitting odyssey and one of the garments she made was a "hap" or traditional shawl from lacework patterns she'd found in the V&A museum, using yarns acquired during her travels in Orkney and Shetland. She was also touched by the number of people who knitted things for her new baby, and grateful that when her daughter Rose was born in summer last year, she was the recipient of so much hand-crafted love.

Inevitably, childbirth brought a temporary halt to Rutter's needlework but she eventually worked out how to knit and breastfeed at the same time and, while she has her hands full with a toddler, she now knits when she can and notes that her technique is much improved thanks to her year of intensive purling.

Although long undervalued, knitting – a craft perfected in candle-lit cottages – is having its day in the sun. But what of its future? Sheep farming has been described by environmentalist George Monbiot as "a white plague" of "woolly maggots" which trashes the countryside. So how might the industry fare if society moves towards eco-conscious, animal-free agriculture?

Rutter acknowledges that the animals are "massively detrimental to the natural environment in that they eat all the saplings". "In Iceland," she adds, "the Vikings brought sheep over and they ate all the trees. But we have to balance that. Which would we prefer: something made of acrylic from the petrochemical industry, which doesn't bio-degrade and releases micro-plastics into the ocean and air? Or something made from wool, which is hardwearing, warm and can be rotted in the compost heap without leaving any footprint? Fleece is a renewable by-product of sheep-farming, which itself is less intensive than cattle-farming in sheds."

As for Rutter's own future, there's another book in the pipeline, though the St Andrews University writer in residence will say only that it's connected to Norway. And she certainly intends to keep on knitting. After 12 months during which she created a dozen garments including Highland stockings and and an English cricket jumper, she is incapable of sitting "haund idle".

Like the fisher women of the East Neuk, she has to be constantly busy with yarn and needles and nor, it seems, can she forget their story. She says she plans to keep working with the Scottish Fisheries Museum, towards establishing what could become a national network of ganseys.

For while she may have poured salt water on the notion that the garment as a kind of knitted shroud, it's clear that Rutter is beguiled by the story of the women who worked on East Fife's shores, crafting intricately-worked cocoons that would keep their loved ones warm, dry and safe from the perils of the wild North Sea.

This Golden Fleece: A Journey Through Britain's Knitted History by Esther Rutter is published by Granta, £16.99. For details of her forthcoming events www.estherrutter.com www.thewoollybrew.co.uk