Shoppers prefer 'vegan' food labels to 'confusing' plant-based terms, according to new survey
(www.veganfoodandliving.com)
The Vegan Society does do certifications for products which will let you use their logo. I'm not aware of any laws which would stop you from calling a product vegan without that certification, just can't use their logo for it.
I can't remember if it was the EU or ISO which was working on a standard to classify a product as vegan in the past couple of years. Though the last news I heard about it was that it was being led by agricultural lobby rather than animal rights activists.