Image caption Vegetarian Laura is delighted she's finally being catered for

"It's all right," is Jordan's verdict on KFC's "Imposter Burger", although he could tell it wasn't chicken.

The 32-year-old would normally choose KFC's standard chicken fillet burger but he has come with a colleague from Medway in Kent to try out the fast food chain's temporary vegan addition to its menu.

"It's a bit lighter," he tells me patting his stomach. He doesn't think he'd have it again, it might leave him too hungry.

I've come to KFC's Gloucester Road, London restaurant, one of 20 KFC branches across the UK trialling the Imposter Burger over the next four weeks, to see what customers make of it. Made from Quorn, a fungus-based meat substitute, it is the chain's first attempt at a vegan alternative to its chicken burger.

Jordan's colleague Laura, a vegetarian, is delighted that she's finally being catered for. She and Jordan both work for the police and KFC is a regular meal break outing for staff. "I felt like I was missing out," she says. "Everyone would go there and I'd just get chips or beans."

Image caption Mujahid Ali had sold 80-90 non-chicken burgers by midday

KFC, best known for its meat products, is the latest fast food chain to jump on the vegan bandwagon.

At the start of the year McDonald's started selling vegetable wraps. Smaller chains such as Byron Burger are offering vegan burgers too, while bakery chain Greggs heavily publicised the launch of its vegan sausage roll. Over in the US Burger King is currently rolling out a vegan Whopper.

The supermarkets are also expanding their vegetarian and vegan offerings, including substitute "meat" designed to mimic the look, smell and taste of the real thing.

Mujahid Ali, working behind the counter at KFC and sporting a green "finger lickin" vegan badge, says business has been brisk. It's only midday and he reckons they've already sold 80 to 90 of the chicken-substitute products. Demand is so high there's a 10 minute wait for my burger order.

When it finally comes it certainly looks like the real thing. But when I bite into it I can immediately tell the difference. It's a bit dry and despite the spices it's bland and unmemorable. I struggle to eat the whole thing.

Image caption Ellen and Sergio both say they'd eat the burger again

Others are less critical.

Ellen, a vegan from Wimbledon in London, thinks the burger tastes fine. "It's not the same but it's good enough for me," the 21-year-old graduate says.

Her friend, Sergio, 20, a vegetarian, says he's always had a weakness for KFC, and he would be happy to buy it again.

The number of vegans, people who do not eat meat, poultry, fish, or any products derived from animals, including eggs, dairy products, and gelatin, only make up just over 1% of the UK population, but the number is growing.

What used to be seen as a rather joyless diet choice is now right on trend, with celebrities such as Ariana Grande and Miley Cyrus talking about avoiding animal products. Meanwhile #vegan has more than 80 million posts listed on Instagram.

There are also growing numbers of people cutting back on meat, with 14% of Brits now describing themselves as flexitarians, those who are primarily vegetarian but occasionally eat meat or fish", according to market research firm YouGov.

More people want to try the vegan lifestyle due to environmental, rather than health reasons, says vegan Instagrammer Lucie Johnson behind the Ugly Vegan account.

"Veganism had a reputation for being an exclusive and expensive diet for yoga mums and hippies; heavily involving expensive salads, whole foods, smoothies and 'buddha bowls'.

The fact that many vegans are no longer choosing the lifestyle for its dietary or health benefits means "lots of us want to eat dirty too," she says.

Image copyright Ugly Vegan Image caption Veganism is no longer just for yoga mums and hippies, says Lucie Johnson

Of course, this trend means some of the health benefits of going vegan are lost. At 450 calories, the highly processed KFC vegan burger is only slightly less fattening then the 475 calorie standard chicken burger. With a fizzy drink and chips that's still almost half your daily recommended intake.

"Well-planned vegan diets can be really healthy. However, just because a product is vegan it doesn't always mean it is the most healthy choice," cautions the British Nutrition Foundation. "It's still important to check nutrition labels."

Abby, a 21-year-old student at Imperial College nearby, has been a vegetarian for nine years and says she'd buy the Imposter Burger again if it stays on the menu. Despite the growing numbers of vegans she says most restaurants still don't put enough effort into alternatives to meat

Image caption Abby said she would eat the vegan burger again

But it's not clear if the burger will stay on the KFC menu permanently. Jack Hinchliffe, innovation director at KFC UK & Ireland, said the "time was right" to test the idea, but cautioned it was only a trial.

"It's early days, let's see how the test goes. We're not going to change our name to KFV [Kentucky Fried Vegan] from KFC," he says.

One of today's customers will be relieved to hear that. When I approach one man to ask what he thinks of his veggie burger, he jumps up in alarm. He had ordered the chicken burger. "I knew it tasted different," he says and rushes off to complain.