ANYONE who thinks veganism is for wimps need only look at David Haye.

The former world heavyweight champion, who recently retired from boxing, turned vegan in 2014 after an injury forced him out of the ring.

He changed the way he did everything – including cutting out animal products from his diet – declaring afterwards, “I think that I’m now fitter than I’ve ever been.”

It seems he’s not the only one to see the advantages of going vegan.

A recent study by comparethemarket.com confirmed what many had suspected – that there’s been a massive increase in the number of vegans in the UK in recent years. A total of 3.5 million people (around seven per cent of the population) now identify themselves as such, and this is up from a previous peak of 540,000 in 2016.

There are three main reasons why more of us are choosing a vegan lifestyle: animal welfare, health and the environment, with the latter gaining traction from videos like Cowspiracy, showing the harm inflicted by animal agriculture. For Will Barker, whose father Mike owns The Health Warehouse, in Darlington, this presented a unique business opportunity. He set up The Green Guerrilla, a mobile catering firm selling vegan street food, two-and-a-half years ago, and has never looked back.

“It was my dad’s idea,” says the 30-year-old, who lives in Darlington. “He noticed that there was lots of street food popping up, but that there wasn’t any vegan. His shop sells vegan and vegetarian food and he put two and two together. We started doing it in his kitchen at work, then we did it in his house, then we went to The Forum, in Darlington, and we rented their kitchen out for about six months. Now we’ve got a unit in Darlington that I’ve converted into a kitchen and bakery. That’s where everything gets made from scratch and loaded up into the vans.”

A former Royal Marine Commando (hence the “Guerrilla”), Will started the business after meeting his partner Hayley and deciding to settle down (they now have two small children). It began with a stall at Durham market and grew from there. “We’ve got Durham market every Saturday and then the farmers’ market every third Thursday,” says Will. “Then there’s the deli in Durham Indoor Market.

“We did so well at Durham market that we just carried on doing it. When we first started, we’d take 250 quid and I’d be buzzing, but now we take much more than that. We’ve got lots of support in Durham. The students are a large part of it – our takings go down a bit when they go on holiday – but the local people do support us as well.”

Perhaps unsurprisingly, the uptake in veganism is highest among millennials, as well as women. Of the 168,000 who signed up for this year’s Veganuary (a Dry January spin-off where people abstain from animal products instead of alcohol) 84 per cent were female and 60 per cent under 35. The trend has been fuelled by social media and vegan celebrity influencers such as Ellie Goulding, Natalie Portman and Ariana Grande.

Increasingly, Will is being asked to cater for mainstream events, including this year’s Hardwick Live, and is much in demand at Durham University. “It’s massive for veganism,” he says. “We did all the summer balls. We have two outside catering units, so we can be in two different locations, as well as an indoor one.”

Veganism isn’t just a diet – it’s a way of life. The Vegan Society, its champion since 1944, states: “Veganism is a way of living which seeks to exclude, as far as is possible and practicable, all forms of exploitation of, and cruelty to, animals for food, clothing or any other purpose.” That means honey is off-limits, as well as wearing leather and watching horseracing.

For Will, it means being sensitive to customers’ beliefs. “Since Sir David Attenborough did Blue Planet, we’ve got rid of our straws in the deli,” he says. “We’ve always been biodegradable apart from that. When customers buy a burger, the majority of them say, ‘You can keep the box. I’ll just take the burger’, but we tell them it’s biodegradable.”

The fact that you can now get a vegan burger points to a shift. Marks & Spencer, Pret a Manger, Wagamama and Pizza Hut (to name a few) have all introduced vegan food and Tesco has even appointed American chef Derek Sarno as director of what it calls “plant-based innovation”.

Will uses vital wheat gluten (a plausible meat substitute) in burgers and kebabs topped with homemade chilli sauce. He also makes vegan sausage rolls, calzone and chocolate brownies – in fact, you name it, he probably does it vegan.

He counts it as a privilege to provide new and tasty options. “It’s great seeing all these passionate people and catering for them,” says Will. “Supermarkets are full of all sorts of alternatives now, so you’ve got to keep ahead of the game and see what’s not being done yet and what you can make vegan that’s not already. It’s also about having a great brand. People see The Green Guerrilla and they recognise it because it’s a quirky name.”

The trend towards veganism only looks set to continue. A recent study by Oxford University cited adopting a vegan diet as the “single biggest way” that people could reduce their environmental impact. It found that cutting out meat and dairy products could reduce your carbon footprint by up to 73 per cent – a much greater amount than by cutting down on flights or buying an electric car.

As more people turn away from animal products, Will aims to cater for them. “A lot of other places are fast food joints or cafés, but I don’t want that,” he says. “I want to keep the street food alive because I enjoy it, but I also want a chain of vegan delis around the North-East and I’m looking to start wholesaling as well.

“A lot of cafés and restaurants that aren’t vegan don’t know how to cater for them, and people want more now. They know what they can have and places have got to keep up with that. It’s so big, there’s no excuse. The only way it’s going to go is bigger.”

W: facebook.com/thegreenguerrilla