When 19-year-old Kaysha Clarius bit into KFC’s hugely successful vegan “Imposter burger” in late June, she was disturbed. A vegan for two years, the mother from Bristol felt the fake fried chicken tasted alarmingly real. “I used to eat KFC, and it was very similar to that,” she says. She stopped eating, took a picture of the fillet and posted it on a 46,000-strong Facebook group for British vegans.

The KFC vegan burger is made from Quorn, a British meat substitute made from a fermented fungus bound with potato protein. The chain is just one of a growing number of fast food outlets offering vegan options. Pizza Hut launched a vegan pizza in January 2018, and the McDonald’s vegan Happy Meal was in its restaurants a year later. Yet, while advancements in the fake meat market delight many vegans, others are concerned that they could, in fact, be eating meat.

“I always get paranoid when [fake meat] tastes so much like the real thing, that one day it’s all going to come out on the news that we have been tricked into eating real meat this whole time,” reads one comment on the Facebook group. In February, a commenter posted a picture of Greggs’ vegan sausage roll, seeking reassurance that it wasn’t real meat. “Had to stop eating,” they wrote. “Please tell me it’s safe.”

Facebook Twitter Pinterest Greggs vegan sausage roll. Photograph: Amy Fortune/Alamy

Thankfully, Greggs had consumers in mind when it designed its vegan roll – an intricate lattice shape on the pastry distinguishes it from the traditional meaty treat. For other products, vegans have masterminded their own tricks: commenters advise waving vegan meat in front of your cat’s nose – if it turns away in disgust, the substance is not the real deal.

Yet, far from being an internet conspiracy theory, concern about fake meat is grounded in reality. At the end of June, a Michelin-starred chef was accused of using chicken stock cubes in his vegan dishes, while in April, a toddler with a dairy allergy had to go to hospital after his parents ordered a vegan pizza for him at Pizza Hut, but he was accidentally given one with cheese.

Clarius posted her KFC burger on the Facebook group because, a month earlier, a woman claimed on the page that a pizza chain had served her real sausage. Multiple pictures in the comment section appeared to show that the pizza the woman received was vastly different from the vegan offering.

Commenters reassured Clarius her burger was Quorn and, after pulling it apart to investigate, she ate it. “The burger had only just been launched, so you wonder if the staff know what they’re doing,” she says. “I’d hope people wouldn’t serve [meat] to vegans [on purpose], but you just don’t know, do you?”