The closure of the schools means that not only will people from London and other English big cities be taking holidays but also people will be having days out from Cardiff, where I know the virus is rife in schools because that's where granddaughter caught it. People are thinking to escape from the virus to areas where there are currently no (or very few) cases. Now it's actually fine for most school age kids and their parents to get Covid-19[*] (unless they have specific health issues), but here in rural Gwynedd, we have a population that skews elderly and fewer ITU beds per 1000 than in England. There's going to be some serious anti-English feeling if people don't use some common sense.
At least one local caravan site has closed and I have a friend who has cancelled all her Air B&B bookings because she herself is vulnerable, but not all businesses are being so careful. We need government action to control the movement of people from one area to another.
[*] Not pleasant, obviously, but not actually dangerous.