When I went into the shop to let them know we’d arrived she went to charge me but I said we were Britstops and she said “oh, you stay for free then” So I assumed anyone could stay if you pay. I’ll see if I can find out more.
Some places are only Britstops, especially businesses that aren’t pubs.
I think it’s worth buying in to the Britstops scheme, around £30 for the book and monthly updates, as you can use the places without buying goods/services if you want or need to. We usually do but there have been times when we can’t or haven’t (like if we arrive/leave before opening or after closing and are just resting to break up a journey, or at the chiropodist’s!). We’ve had some great destinations in their own right where we’ve eaten, stayed over, used their car park all day, gone for a long walk and returned for drinks/snacks/tea/dinner before leaving if they’re open. Hosts are usually very friendly and most of the places feel really safe. As long as you remember you’re not camping, just parking and kipping in the van all’s good (some like this farmshop though don’t mind people picnicking, sitting out).