Depends on the quality of the food and your plans.
Cambridge for example has a couple of places where vans can gather or cook in public places i.e. at bars/coffee shops with no food and also ‘food park’ where someone arranges a gathering on farm land or similar.
There’s a burger van I won’t mention the name as it’s already popular enough (and I don’t like to share) that anchors outside a coffee shop in town and has a second van too. There’s always a wait for the food and they only sell burgers and fries and very little else. But once you have one of their burgers you’ll realise a) why it costs about £7, and b) that you will forever be disappoint in any other burger you eat as it won’t be as good.
Festival only, you need to make good food these days as there’s plenty of competition!