David Morse is suddenly apologetic. A wounded calf has returned from the vet unexpectedly early and he must tend to it immediately, interrupting our phone call. The calf is months old and has had a "very nasty" fall, snapping her leg clean in two. The farmer is desperate to see how the wound has healed and if the "poor lass" is recovering.

David has worked his 500 acres of land in County Durham for the past 40 years, and often – like most within the agricultural sector – is woken at 2AM by a rogue cow or a wandering hen.

However, I'm not on the phone to discuss any of that. The reason I'm talking to David is because I'm wondering what might happen to people like him if the relentlessly-growing trend for going vegan continues. In 2016, a study found that at least 542,000 people in the UK are vegan – a 350 percent rise on ten years before. Yes, that number accounts for just under 1 percent of the country's population, but let's assume it keeps growing exponentially and, 50 years from now, we exist globally on an exclusively plant-based diet, like in that Simon Amstell show, or Heather Mills' wildest fever dreams – no production, no exportation, no nothing.

What happens to the UK economy? What happens to all those meat and fish-related jobs?

According to the Department for Environment, Food and Rural Affairs (DEFRA), approximately 500,000 people in the UK work within farming "enterprises", including both livestock and arable / horticultural farmers. The latest figures show that over 17 million hectares of UK land are currently farmed, and that, in 2016, more than 10 million cows, 33 million sheep, 4.9 million pigs and almost 173 million poultry animals were reared by British farmers.

With our largely omnivorous population, those animals produce a tidy profit for the British economy. Currently, farming and agriculture contributes about £24 billion of revenue, and £8.5 billion of Gross Value Added, to the UK economy, not including the food, service and hospitality industries that are also affected by the productivity of British agriculture. While this industry only directly accounts for 1.35 percent of the British workforce, it largely exists in concentrated areas. According to George Dunn, Chief Executive of the Farming Tenant Association, there are several areas of the country (parts of the Lake District and the Welsh uplands, for example) where "livestock production is the only feasible industry you have – you couldn't do anything else".

The fishing industry is much smaller, with 12,100 active fishermen working in 2015, and UK vessels landing a total of £775 million worth of fish.

WATCH: How to Make the Best Vegan Sandwich

Sean Rickard is a former economic advisor to the European Commission on all things farming and food-related. I ask him, roughly speaking, how many jobs would be at stake should we all go vegan. "You're looking at about 100,000 to 200,000 livelihoods," he says, "then you've got other areas that would be affected, such as tourism, foreign trade and, of course, the food industry."

Given that "food and drink is the UK's largest manufacturing sector", if we erased the majority of Britain's dietary staple, surely the food industry would face a massive hit? "Yep, probably around 100,000 jobs in food industries. Over time we'd find a way to replace them."

"Economically speaking," says Sean, "sales of food and drink in Britain are about £200 billion, per year. You would have to replace all the meat and dairy, which it simply wouldn't be possible to do. We'd have to import a hell of a lot of food, which would be a hell of a cost to the economy – probably around £50 or £60 billion per year."

The latest figures support Sean's theory that, even if we did manage to produce shed-loads more plant-based products ourselves, they simply don't make as much money. Figures from DEFRA show that farmed crops contributed about £8 billion to the UK economy in 2016, whereas livestock output (including milk and eggs) generated around £12.7 billion. Not that the livestock farmers get to see much of it.

"Farmers are increasingly squeezed by large retailers, who push unfair pressures through the supply chain," says George Dunn. "It's really tough to earn a living; we have lots of families who are using tax credits to get by."

Only 16 percent of farmers earn an average salary of more than £50,000 a year. The general picture for livestock farmers is much more modest, with an average annual salary of £20,000, or £16,500 if you're in Wales. Purely plant-based farms, however, take home around £30,000 to £60,000 per year. Hence, if we all went vegan, it wouldn't be the wealthier farmers feeling the pinch.

"You'd be hitting the small-scale farms, which many want to keep in the countryside," says Sean Rickard. "Small-scale farmers can only entertain livestock. To farm arable crops, you need much more land and bigger, expensive machinery."

Beyond the farms themselves exist entire communities that, without livestock produce, would be pretty much destroyed. "Rural communities and rural farms would be totally crippled," says Michael Oaks, dairy farmer and Chair of the National Farming Union Dairy Board. "There's a whole raft of small dairies in the countryside that would go out of business, and I have at least 35 different companies that supply me with all sorts of things, from bedding for cows, to fencing, to feeds. Every year, I spend hundreds of thousands within the local community."

As well as the local corner shops, Michael's milk supplies butter brands such as Anchor, Arla and Cravendale – which would also take a hit in an alternate vegan universe. "There are people in the food processing industry that rely on us for the raw materials," says Michael. "If you take the farms out of rural economies, they will die. Nobody will make any money, so no one will go to the pubs because they won't be able to afford a pint."

Photo: Flickr user Takver, via

A fourth generation farmer, Anna Longthorp has tended to pigs and cows on her family's farm in east Yorkshire since she was old enough to walk, and now runs her own pork-specialist enterprise and butchery, Anna's Happy Trotters. "I've always been interested in the pigs," she says, chirpily. "They were far more interesting than crops – and I absolutely love them."

When I put the question of job losses as a result of a national veganism epidemic to Anna, she lists a load of professions I hadn't even considered – a collection of professions involved in producing livestock and animal produce that's of a high enough standard to sell: "Holliers; abattoir assistants; agronomists; drainage engineers; forage nutritionists; vets – there would be a massive impact on job losses," Anna says.

David Morse has a similarly horrified reaction when I ask him the same question.

"The labour force would be hugely reduced," he says. "We'd have to turn to mechanical farming instead. There are so many businesses involved with our farm in order to get to the end product. The local vets, for instance, specialise in livestock. We have about 20 to 30 wagons coming onto the farm every day to supply us with something or other."

Pig farmer Anna informs me there are people literally employed to trim cows' hooves. There's an on-call rat-trapper for most farms, and even a professional chicken sexer, hired to distinguish the sex of chicks.

But if we spared the lives of God's creatures in favour of a plant-based diet, surely such jobs would simply be replaced with a niche, plant-specialist workforce? Not quite. Unfortunately, it wouldn't be as simple as everyone just switching to growing crops, partly because there just wouldn't be the demand, and also because the British countryside can't accommodate it.

Dr Jude Cappa is an animal scientist and Livestock Sustainability consultant, and is often called upon by the food industry to advise on environmental issues. As someone who spends her time uncovering the myriad ways in which animal rearing aids the environment, she finds the prospect of an entirely vegan society "very, very frightening".

"Yes, cattle does release methane, but the benefits for the environment of grazing livestock far outweighs the costs," she says. "It's fantastic for the bio-diversity of the land – we can now use much more of the land than we used to be able to as a result of grazing. Farming animals may actually be better for the carbon footprint. Without animals, you'd have to use manufactured fertilisers, which means using more fossil fuels and chemicals."

"Not only that," she continues, "but the land isn't suitable for us to farm other things."

According to Sean Rickard, it would be almost impossible to farm purely arable crops in about a third of the British countryside, due to the under-nourished nature of the land. "Roughly speaking," he says, "if you draw a line from Edinburgh to Southampton, we've always grown plants to the right and reared meat and dairy to the left." Growing crops on hills is pretty much impossible, so you'd end up with "half the country with nothing growing". Not only would the land be bare, but it would get pretty ugly, too. According to The National Trust: "The rapid reduction of livestock farming would be disastrous for cherished species or habitats."

The Agriculture and Horticulture Development Board produced a report recently that detailed what would happen to the great British countryside without livestock farming. To name a few potential repercussions, you'd see: a loss of trees and wildlife; large areas of bracken, scrub inhabited by dormice; scatterings of granite boulders; wild, unkempt feral animals; and mass flooding due to dilapidated fencing. As it turns out, much of the UK's landscape as it stands today is a direct result of British livestock farmers – and their animals, of course.

"You need animals to keep the grass down," says Sean. "In short, you need animals to keep the countryside going."

UPDATE 20/09/17: A previous version of this article stated that chicken sexers are hired to encourage chickens to mate, when actually they distinguish what sex a chick is.