Concerns over some meat substitutes and vegetarian meals were raised in June with US researchers reporting severe adverse reactions to the fungus-derived mycoprotein used in Quorn meat substitutes. Meanwhile, Britain’s Food Standards Agency (FSA) was investigating allegations that traces of meat were found in “meat-free” and vegan meals sold at the UK's two largest supermarkets, Tesco and Sainsbury’s.

According to Reuters, the FSA statement followed a Daily Telegraph newspaper investigation, which detected traces of turkey in a Tesco vegan macaroni ready meal and traces of pork in Sainsbury’s “meat-free” meatballs.

Sales of vegetarian and vegan products are rising in the UK, with one in 10 shoppers in Britain buying a meat-free ready meal in January 2018, according to research firm Kantar.

Sainsbury’s said that the meat-free meatballs were made at a meat-free factory and that it carried out regular checks and had found no issues. “We are concerned by these findings however and are carrying out a comprehensive investigation alongside our supplier,” the supermarket said.

Tesco said it had carried out initial DNA tests on the product in question, its BBQ Butternut Mac and found no traces of animal DNA in the product. “We take the quality and integrity of our products extremely seriously and understand that our vegan and vegetarian products should be exactly that,” Tesco said.

The Telegraph sent ten different food items to a German-government accredited food testing lab which carried out tests for eight types of meat.

According to a paper published in the Annals of Allergy, Asthma & Immunology by researchers from the Center for Science in the Public Interest (CSPI), mycoprotein—the fungus-derived substance that forms the basis of Quorn-brand meat substitutes—appears to cause sometimes life-threatening allergic and gastrointestinal reactions, and health officials should consider whether the products should be permitted in the food supply.

In 2002, alarmed by an early company study submitted to the US Food and Drug Administration demonstrating adverse reactions to Quorn, as well as by independent research, CSPI started collecting adverse reaction reports from affected consumers.

"Of 1,752 such reports analyzed for the study, 312 reported allergic reactions, including hives, itching, and difficulty breathing or swelling of the throat, tongue, mouth, or lips. Ninety-two, or 29.5 percent, of those people, reported seeking medical attention. A total of 1,692 people reported gastrointestinal reactions, such as nausea, vomiting, diarrhea, or cramping. Some suffered both allergic and gastrointestinal reactions," CSPI said.

An 11-year-old boy with a history of mold allergy and asthma, Miles Bengco of California died after a Quorn Turk’y Burger allegedly triggered an asthma attack, according to the paper.

“Physicians, health departments, and lay allergy organizations should be aware of this possibly under-recognized mycoprotein-associated cause of adverse reactions,” wrote Michael F. Jacobson, co-author of the paper and CSPI co-founder and senior scientist, and former CSPI research associate Janna DePorter.

The mold processed into mycoprotein is a distant relative of edible fungi, and Quorn dropped mushroom references on Quorn packages and labels. In 2017, as part of a legal settlement, it agreed to a package warning that: “Mycoprotein is a mold (member of the fungi family). There have been rare cases of allergic reactions to products that contain mycoprotein.”