The data was obtained by a foundation set up by the parents of Natasha Ednan-Laperouse, who died after eating a Pret a Manger baguette.

Owen Carey, who had a dairy allergy, suffered a fatal reaction after consuming grilled chicken coated in a buttermilk at Byron burger.

Symptoms of an allergy range from skin redness and swelling to - in the most severe cases - vomiting, diarrhoea and anaphylaxis.