Artisan bakers have set up shop all over the UK, and many use the same coarse, creamy, stone-milled flour from Shipton Mill. What is so special about it?

Britons' love of breadmaking has grown and spread over the past 15 years, like an unstoppable loaf spilling out of its tin. Artisan bakers have opened in nooks and corners all over the country, tucked into east London railway arches or Scottish crofts.

I am a carbohydrate pilgrim. In a typical month I visit bakers all over London. Peeping under the counters, the stiff, papery flour sacks all say the same thing: Shipton Mill. Could it be that this mill is at the centre of artisan baking in the UK?

I decide to call a baker's dozen of UK bakers and ask where they buy their flour. "Shipton Mill," says Mark's Bread in Bristol. Ditto the Forge Bakehouse in Sheffield, Pullins in Clevedon and Earth's Crust Bakery near Castle Douglas in Dumfries and Galloway. Bakers can be slow to pick up the phone (hands dusty with flour) but they are good at returning calls, so in the end the sample has grown to 17. Other brands of flour crop up – FWP Matthews, Marriage's, Doves Farm – but 10 of the 17 bakers buy flour from Shipton Mill, owned by John Lister.

"It is the Prada or Gucci of flours," says Lisa Brook, director of Flour Power city bakers in London. Tom van Rooyen from Earth's Crust says the flour is such a distinctive creamy colour, "slightly coarser than a standard flour", that he could tell it by sight and touch.

Dan Lepard, a baker and food writer, says that when he started the bakery at St John restaurant in London in 1994, "one of the first people to come and see me was John Lister. He travelled all the way just to say: 'Here's my flour, what do you think of it?' He has been doing that with bakers around the country for years."

Shipton Mill in Long Newnton near Tetbury in Gloucestershire.

Shipton Mill is hidden away up an unnamed road past the village of Long Newnton near Tetbury in Gloucestershire. The greens of the lawn and surrounding fields are darkened by recent rain. Lister has owned the mill since 1979. When he bought it he knew nothing about flour; he had studied anthropology. But in his early 20s, his grandmother took him to visit a watermill in Felin Geri, west Wales. "I was so struck by the process, I thought: I'm going to do that." He bought the equipment from a run-down mill before he found, "for a very, very small amount of money", a mill to put it in. In the 30 years since, Shipton has gone from serving "a handful of local customers" to being the foremost stoneground mill in the UK.

"Bakers are gods now," says Lister. He enjoys pointing out that "le pain se lève" (the bread rises) was allegedly the greeting of peasants in a 14th-century French revolt. Anyone can bake: baking is like seizing power. "To make bread you need your hands, you need some salt, you need some flour … a small oven," he says, all the while drumming his thumbs and pushing his hands over the surface of the glossy boardroom table, as if he is kneading his thoughts. "There's a culture of 'I want to do it, I can do it, I don't need a business plan, I don't need lots of money, I don't need a bank.'" Witness his friend, who bakes in a container on a timber yard, or Van Rooyen, who started out making 20 loaves a week and now makes up to 300.

So why is his flour so special? "In old baking, the dough was simply a carrier to hold other flavours," says Lepard. "By 2005 or 2006, artisan bakers started to say: 'Well, is there more to sourdough than sourness? If we are taking everything back to its basics, then surely the flour matters as well?' Now the new thing is to get more of a wheat flavour. They can be nutty, grassy, sweet, even a little bit bitter, like a great beer. All of these flavours you will find in traditional stone-milled flour."

And each loaf contains something of the story behind the flour. "People have been milling here for a thousand years nearly," Lister says quietly, as if their ghosts may be listening. He searches for the wheat himself. "We try to find the extraordinary," he says. "You know it immediately when you see it. You just want to jump into it. It smells like … a smell that you'll know even though you've never consciously smelled it. You'll know that that's summer and it's absolutely perfect." But he is not responsible for any baking revolution. Isn't he being too modest? "No," he says. "You just make flour and you talk to people you like and everybody helps grow it." He smiles, pushes the heels of his hands over the table again. "And le pain se lève."