If a devote vegetarian was given and actually eat some meat in a restaurant , after specifically discussing and ordering a veggie meal, could you sue the restaurant?
I would think you could do something but it'd be a hard case to win.
Get in touch with trading standards for advice-get number from yoru council.
But do you have any evidence/food from the incident?
As if not you haven't got a leg to stand on as it's your word against theres.