A couple of weeks ago, some eye-catching billboards began appearing around central and east London. Entire tunnels of the underground were plastered with the adverts; the sides of large buildings were covered. On one panel there was a carton (or, in some instances, three) of Oatly, an oat drink made by a cult Swedish company that favours stark graphics, a bluey-grey colour scheme, and which is a market leader – in a not uncompetitive field – in the tongue-in-cheek promotional messages known as “wackaging”. The adjacent panel, in large, wobbly type, read: “It’s like milk, but made for humans.”

Around the same time, during commercial breaks on Channel 4’s 4oD, there appeared a 15-second clip of a man in a field of oats, playing a tinny 1980s synthesiser and howling: “Wow, no cow!” That guy is Toni Petersson, the 50-year-old CEO of Oatly, and the song, you would not be entirely surprised to learn, is his own composition. “Listen, it’s absolutely terrible, right?” says Petersson, over the phone from Eugene, Oregon. “My creative directors wanted to make some commercials that I was part of. One of them included a song that they wrote, which was even worse. I had no idea; I thought it was going to be shown one time only.”

“Milk, but made for humans” reprises a campaign that his company used in Sweden in 2014. That led to the Swedish dairy conglomerate LRF Mjölk taking Oatly to court for vilifying its product. LRF Mjölk won the case, Oatly was banned from using the line and had to pay around £100,000, but there was a curious collateral effect of the lawsuit. The resulting publicity – stoked by Petersson taking out full-page adverts in newspapers – helped Oatly’s sales rise by 45% in Sweden and made its profits spike.

Petersson, who previously worked in nightclubs and Costa Rican real estate, became Oatly CEO in 2012. So is he fearful of – or even hoping for – a similar battle in the UK now? “There might be some legal consequences, I don’t know,” he replies. “But am I concerned about it? No, I’m not. It’s just true!” Petersson laughs. “We actually have really, really good lawyers; they really enjoy this too. I mean, who could argue with the fact: ‘It’s like milk, but made for humans?’ How can that be wrong?”

Many people seem to agree with Petersson: another Oatly campaign calls these folk “the post-milk generation”, and sales of plant-based drinks or “alt-milks”, to use the sassier terminology, are having near-vertical increases. So who are they? There are vegans, of course, who now make up 1% of the British population (or 600,000 people). Also, those who have a milk allergy or lactose intolerance. The line “made for humans” comes from the observation that we are the only mammals that consume milk past weaning. Around two-thirds of the planet has a reduced ability to digest lactose after infancy (though that figure is much lower for people of European extraction). Mark Kurlansky, the author of a recent history, Milk! A 10,000-Year Food Fracas, describes the fact that many adults drink milk as a “defiance of a basic rule of nature”.

But the surge in popularity for alt-milks has many different sources. There are those who are concerned about animal welfare or our perilous environmental situation: recent research found that a quarter of us now consider ourselves “meat reducers”. In October, a major study on our food system published in the journal Nature advised that prosperous countries such as Britain and the US should cut their milk consumption by 60% (and beef intake by 90%).

A mural advertising Oatly oat milk in Brick Lane, east London.

Photograph: Nathaniel Noir/Alamy

Then there are people who have never much liked drinking milk, or who don’t buy the health claims that resolutely cling to it. Or maybe they just want to try something different. Oat drinks, which tend to taste quite neutral but still creamy, can often be a gateway for those thinking of converting. Oatly, in particular, dominates the market of specialist coffee shops, especially in Europe and the US. This summer, the New Yorker reported that New York was experiencing a critical shortage of Oatly, which began supplying a handful of coffee shops in the city in 2016 but expanded rapidly to more than 1,000 outlets nationwide. A litre of Oatly was selling for $20, five times the regular price.

I suggest to Petersson that this might have been another publicity stunt: creating scarcity and fanning interest. “Oh, I wish it was,” he says. “I wish we were that clever.”

Beyond oats, the options are almost overwhelming. Rude Health, Britain’s leading organic, dairy alternative brand, began selling drinks in 2013: it started with oat, brown rice and – almost as an afterthought – almond. This turned out to be a sound move; Rude Health’s Almond Drink is its bestselling item in any category and it is estimated that two-thirds of the alt-milk sold in Britain is almond (one of the main drivers, apparently, was Gwyneth Paltrow, who extols its virtues in her recipes and on her wellbeing site Goop). Rude Health now makes 10 drinks, including exotic offerings such as hazelnut and calcao, and tiger nut, which is not actually a nut, but a tuber.

Meanwhile, Innocent – the birthplace of “wackaging” (infantilised, overfamiliar packaging), and since 2013, owned by Coca-Cola – moved into dairy-free drinks earlier this year (its slogan: “You ain’t seen nuttin’ yet”). It has a range of four – almond, oat, hazelnut and coconut – and makes much of the fact that its almond and oat drinks only contain the named ingredient plus spring water and salt.

Several companies make creative use of misspellings and asterisks in their branding: Rebel Kitchen goes for “mylk”; in the US, there’s organic “malk”; while if you live in London, you can have, for example, Pistachio and Sweet Chai M*lk delivered to your door in reusable glass bottles by the M*lkman. The M*lkman is Jamie Chapman, a former photographer who lives in east London and packs his drinks with a market-leading 12% nuts. His pitch: “M*lks to get you off.” (The reason for the subterfuge is last year’s EU court ruling that determined only liquid from animals can be called “milk”. A similar legal kerfuffle in the US resulted in Dr Scott Gottlieb, the commissioner of the Food and Drug Administration, making a memorable distinction in July: “An almond doesn’t lactate.”) It seems only a matter of time before we see the widespread return of the milk, or m*lk, float (electric of course).

Rude Health founders Nick and Camilla Barnard, who have ‘something close to sympathy’ for milk.

Likewise, whereas once you might, if you were lucky, have found soya in a vegan-friendly cafe, now alt-milk has gone mainstream. Starbucks, the world’s largest coffee chain, has not failed to take note of the trends coming out of the smaller, third-wave coffee shops, where idiosyncratic requests are a point of pride for both customer and barista. It is rapidly supplementing its plant-based menu and now offers coconut, oat, almond and soya “milk”. It’s hard to measure the impact of Instagram – specifically “latte porn” – but everyone agrees it has been influential in spreading the word, especially with a younger crowd.

The “post-milk generation” are a fast-growing army. Alt-milks have established themselves in a way that “alternative” products never have (sorry, Quorn). Oatly’s UK turnover in 2017 was £9.5m, an increase of 60% on the previous year. Similarly, sales of Rude Health’s dairy-free range is growing 44% year-on-year. In 2018, it is projected that its growth will be 100% to £19m, while its global turnover rises to £85m. In America, in particular, it seems they can’t get enough of it: the prospective production Oatly plant in Oregon would serve the west coast just as the finishing touches are being put on one in New Jersey for the east. Similarly, sales of Rude Health’s dairy-free range is growing 44% year-on-year.

“This is not a trend,” says Petersson, “this is a paradigm shift. And what’s driving it is young people. It’s a true concern about climate change, animal welfare, ethical food production – those are huge topics. Because [young people] know that they are going to inherit all the shit we’re going to give them.”

Petersson doesn’t mind playing the fool in his ads, but his intent is very serious: in his lifetime, he believes, sales of alt-milk will overtake regular milk. “No, this is not going to stop,” he says. “The state of the Earth, the planet… So I’m absolutely convinced that it’s going to outgrow milk for many years. And some day – maybe 10, 15 or 20 years – it’s going to become as big as dairy. I’m 100% sure.”

Traditional, regular milk, probably derived from a cow, faces quite a battle then. But this is nothing new. Mark Kurlansky, who has previously written books on cod and salt, calls milk “the most argued-over food in human history”. There have been – and remain – impassioned debates over, among others, the benefits of breastfeeding, which animals we should and should not milk, the safety of “raw” milk, the health benefits of pasteurised. Many of these have been taking place for many thousands of years.

“If you think about it, it’s not surprising people argue over it,” Kurlansky tells me. “What is it? It’s bodily fluid that mothers produce for their young. I’d have loved to have been there the first time there was this baby and either the mother had died or the mother wasn’t able to produce milk and they are all standing around saying, ‘What are we going to do? We’ve got to get milk for the baby.’ And somebody says, ‘What about that goat over there?’ I mean, what an extraordinary moment!”

Still, the fact that humans have been drinking milk for 10,000 years does give its defenders a solid base to return fire to their new challengers. “What I would say to you is that, in the UK, 96% of households still have milk in their fridges and still actively buy milk,” says Dr Judith Bryans, the chief executive of Dairy UK, which represents farmer-owned cooperatives and private dairy companies. “The figures have been relatively consistent since around 2012. So this idea of everybody’s turning away from dairy is not really true. We’ve also got 94% of British households actively consuming cheese, and 78% consuming spoonable dairy yoghurts. When you have figures like that in front of you, it tells a slightly different story to the one that some people would like to tell.”

Bryans has seen Oatly’s new advertising campaign and, unsurprisingly, she’s not impressed. “What is fascinating, to me, is that plant-based drinks market themselves on dairy values,” she says. “If your product is really strong as a product in its own right, why do you need to market yourself on the basis of the virtues of another product that already exists? In terms of the idea about ‘milk, but made for humans’, I have a PhD in nutrition and people have been consuming milk and dairy products for millennia. They’ve been consuming them for a variety of reasons: for nutrition, for their versatility, for the taste, for the benefits they give.”

Milk is an extraordinary, incredibly complex substance, but we’ve reduced it to red, blue or green

Kurlansky, too, doesn’t entirely buy Oatly’s line. “Yeah, but who says humans are supposed to drink oats?” he says.

Also, milk alternatives are not without ecological concerns of their own: it takes around a gallon of water to grow a single almond; California, which produces 80% of the world’s almonds, was in drought from 2011 to 2017. In the midst of that catastrophe, Mother Jones magazine put it bluntly: “Lay off the almond milk, you ignorant hipsters.”

Still, alt-milks are more healthy for us than milk, no? Bryans won’t concede the fight. “A lot of people talk to us about wanting to have clean eating and to have natural food,” she says. “So pick up a carton of milk, it contains 100% milk. And you have a whole combination of nutrients in there from high-quality proteins to calcium to iodine, and B vitamins. It’s a naturally nutrient-rich package.

“Now,” she adds, “you turn around the carton of that plant-based beverage and what you tend to have is a very small percentage of the plant, and then you have colourings, preservatives, additives, and usually fortification of vitamins and minerals that already exist naturally in milk.”

When you read the alt-milk cartons, Bryans does seem to have a point. Most plant-based drinks contain oil (typically rapeseed or sunflower) to give the creamy feel we get from milk. Almond milk is typically only 6% almonds, and often just 1%. Part of the reason the Oatly brand is so beloved of baristas is that it is “microfoamable”, like regular milk, and does not separate when you add it to coffee. This, though, is because the company adds an acidity regulator.

For these reasons, Bryans thinks that alt-milks (which typically cost between £2 and £3.50 per litre) will be exactly what Oatly’s Petersson insists they are not: a fad. “You grow up with milk in your childhood, it’s your friend, when you’re expecting your own child, all through your adult life and into old age,” she says. “Alternative products are the trendy friend you go clubbing with but you break up with them really often. So you might flirt with one kind of plant-based drink, then another kind, but milk is the one that sticks with you throughout your life.”

And yet, despite our long, mostly monogamous relationship with milk, some undeniably significant societal and demographic changes are taking place. In the UK, some estimates suggest that dairy consumption has fallen by 30% in the past two decades. While over-65s were found to drink milk 875 times a year, young people (aged five to 24) only did so on 275 occasions.

Part of the reason for this shift, unquestionably, is that many of us have lost faith that drinking milk is doing us good. Milk does contain calcium and vitamin D, but whether this leads to stronger bones, as our parents assured us, is controversial and contested by some recent studies. It’s packed with protein, which is essential for the growth and repair of the body, but in the UK, most people already consume more protein than they need.

“There’s all these myths about milk being healthy,” says Kurlansky. “A lot of it isn’t true and a lot of people have been drinking milk, and not particularly liking it, because they thought that they should. And so now they realise they don’t have to and they are glad not to.”

When I meet Nick and Camilla Barnard, the founders of Rude Health, at their HQ in west London, I expect them to talk down milk. Instead, strangely, they have something close to sympathy for it. And actually, they really like it – at least in its raw, unpasteurised form. Nick Barnard even reminisces fondly of winning the World Porridge-Making Championships in 2013, using raw Guernsey milk and cream from a dairy in Somerset that he had to “smuggle” into Scotland, because they are outlawed there.

“Milk is an extraordinary, incredibly complex substance, but we’ve reduced it to red, blue or green,” says Camilla Barnard. “And the supermarkets fight over how low in price it can be. We’ve just pasteurised it, we’ve homogenised it, we’ve made it as cheap as possible – bang it out there. And then, surprise, surprise, we’ve gone off it. We lost all the value in it, which is really sad.”

While Dairy UK’s Dr Bryans is technically correct to say that milk is just “100% milk”, that statement does simplify the process it takes to be delivered from a cow to our table. No one disagrees that pasteurisation, which came in at the end of the 19th century, was a life-saver, but you do lose something when you heat milk to just below its boiling point and rapidly cool it: namely bacteria, both good and bad. And when you standardise milk (mix it with milk from other cows, other dairies) and homogenise it – to remove surplus fat, sugars and protein that are over the minimum specification – you do change its nature. For Nick Barnard, this is most obvious in its colour: milk from a just-milked cow is yellowy; nothing like the gleaming white that blinds us from supermarket fridges.

The Barnards believe alt-milks are thriving because they offer something different. “We just felt consumers were ill-served by choice,” says Nick Barnard. “So we came in with a pizzazz, we came in saying, ‘This tastes great! You can bake with it! You can make smoothies! You can make horchata!’ So all of a sudden, it was just more joyful. It’s not misery: ‘I can’t have milk.’ If you like almond, then have almond; if you like gold top, and you’re not lactose intolerant, then have that. Celebrate diversity.”

He agrees with the dairy lobby that it doesn’t make sense to directly compare milk and plant-based drinks. “At the end of the day, almonds and water have the nutritional value of almonds and water. The value of raw milk is that it’s a food” – that is, nourishing and sustaining on a deeper level.

“Our work is to not encourage anxiety: ‘You must have this dairy-free, because dairy is going kill you!’ Or: ‘Cows are going to destroy the world.’ No! What you need to do is to say: ‘What suits me?’ And then: ‘Does it make me feel good?’”

Some of Rude Health’s milk substitute products.

David and Wilma Finlay are dairy farmers with a medium-sized holding in Dumfries and Galloway, not far from the English border. They run the Ethical Dairy and are trying a new approach to cow’s milk. They have “110-ish” cows that are hybrids of three breeds designed to create a more robust, productive and long-living animal. “Our cows look like liquorice allsorts – they are all kinds of colours and shapes and sizes,” explains David Finlay. “There’s a lot of bonuses that come from crossing, but they don’t look so pretty.”

For much of the past 25 years, the Finlays have been turning the milk from their cows into ice-cream, but they recently began to concentrate on making artisan, raw-milk cheese. But that’s not what is really radical about what they are doing. A couple of years ago, the Finlays started to wonder if they could make their farm work both as a business and an ethical enterprise that puts animal welfare at the heart of the operation. At the centre of the experiment was the idea to allow calves to stay with their mothers for five to six months after they are born. The cows are still milked during this period, but only once a day.

Some background might be helpful. In most commercial dairies, calves are taken away from their mothers soon after birth; organic farms are required to keep them together for a minimum of 24 hours. On the most intensive dairies, cows will be milked three times a day. In these industrial facilities many cows don’t survive to the age of five.

The Finlays’ experiment began in October 2016 and David admits the first year did not go well. The farm was “haemorrhaging” money and the cows were discombobulated. “We were all stressed about when were they going to see the calves again,” he explains. “Every time we came into the parlour: were the calves going to be there? They didn’t know what the rules were any more. The rules had changed.”

Decades of industrialisation mean that it’s hard to imagine supermarkets telling us that a pint of milk is actually £2

Finlay was ready to give up but his staff talked him round. He’s pleased they did: year two has just come to an end, the milk yield is back up and the cows are thriving. “OK, we’re still not profitable,” he says, “but we’re on our way to a profitable system.” One of the benefits of a less intensive system is there is much less pressure on the cows, so they in theory live longer. There’s evidence of this already on the Finlays’ farm, which converted to organic around 20 years ago: their oldest milking cow is nearly 18, and the average is around nine. Also, in recent years the Finlays have reduced the farm’s greenhouse-gas emissions by more than half, one of the least defensible aspects of dairy farming.

Moreover, the public seems to like what the Ethical Dairy is doing. The Finlays recently launched a crowd-funding campaign to raise £50,000 with an aim to “revolutionise the dairy industry”: their hope was to share what they’ve learned and make ethical farming open source. They achieved their target with days to spare.

“We listened to our customers and said, ‘OK, we’re going to give it a go, will you come with us?’” says David Finlay. “Because no one else in the industry is going to help, no one in government is going to help us. And it really is quite amazing how that has reverberated.”

Is there a model here for the future of dairy farming? Would customers – even the younger generation – return to milk if they had a guarantee that everything had been done to make its production as ethical, sustainable and environmentally considerate as possible? That all efforts have been taken to make the end product as delicious as it can be? It’s difficult to predict if this could work on any scale: a few farms in the UK have a similar system to the Ethical Dairy, but it is by far the largest. And there is another problem: price. It’s often pointed out that milk now costs less than a bottle of water. Decades of industrialisation and commodification means that it’s hard to imagine supermarkets suddenly telling us that a pint of milk is now actually £2.

Even David Finlay does not think that price rises are the answer. “It’s a very difficult one. People say, ‘Well, we’d be happy to pay 10p a litre more – that’s not a big issue for us.’ But you think, if the farmer was getting 10p a litre more, I know what would happen. My neighbour who has got 1,500 dairy cows, he’d put up a shed tomorrow with 500 more cows in it. Whereas your 100-cow guy couldn’t afford to put up a new diary premises for more cows. OK, he would benefit but almost immediately there would be too much milk in the market and the price would come down. So the price is only one factor in the whole food cycle.”

More likely, in the future, we will see a more extreme version of what we have now. “With milk, as with almost all food, two separate markets are developing: rich, urban people and everybody else,” says Kurlansky. “It was actually a Welsh farmer who said to me, ‘The future of high-quality milk is in cities.’”

Suddenly what you splash on your cereal in the morning or dash in your coffee has become very complicated. Regular milk is too commodified; alt-milk is not nutritious enough; raw milk, to use an often-quoted line, is like “playing Russian roulette” with your health. But, as with many aspects of modern life, the outlook is not relentlessly gloomy. Never have there been more options to choose from. If you want to find a dairy committed to ethical practices, they are out there. If you want to use M*lk, made from a “nut” (but really water flavoured with an edible tuber), that exists too. And if you’re happy to ignore the incongruity of pouring another animal’s milk in your tea, then the shops will still stock your blue, green and red for a while yet.