They don't specifically say it is, but from the ingredients list it looks ok:
from
http://www.burgerking.co.uk/pdfs/ingredients.pdf
Beanburger patty
Cooked Red Kidney Beans (31%), Breadcrumbs (14%), (Containing Wheatflour, Raising Agents
(E450/Diphosphates, E500/Sodium Bicarbonate), Yeast, Flour Improvers (E300/Ascorbic Acid, E920/L-Cysteine),
Carrot (10%), Onion (9%), Potato Flake (Containing Emulsifier (E471/mono-and Di-Glycerides Of Fatty Acids)
and Preservative (E223/Sodium Metabisulphite), Rapeseed Oil, Batter (Contains Stabiliser E412/Guar Gum),
Green Peppers (7%), Water, Green Chillies, Salt, Chilli Powder, Garlic Puree, White Pepper.