Toilet accessibility in the UK

Hi everyone.
I'm heading to England on vacation in July. I'm just wondering how easy it is to find toilets while out touring. (I'm from Canada).
We are spending a week driving around Devon and Cornwall, and a week in London.

I'm mostly concerned about the week in Devon/Cornwall, as we'll be out exploring the villages, beaches and walking in the national parks. My UC had been in remission, but is getting worse lately (frequent BMs, urgency, accidents). Heading to the doctor to see if i need to try new meds, but that can take time.

Is it easy to find toilets in gas stations or shops? Starting to get a little anxious about the trip!

Thanks!

Villages aren't likely to have any public toilets except in pubs or cafes. I haven't been to Cornwall but it's touristy, so there's likely to be plenty of cafes and tea shops knocking about. And even the smallest village will usually have at least one pub.

Small shops don't usually have toilets available to the public, though large department stores and supermarkets will. Not sure about petrol stations really - don't think so, by and large.

Basically, anywhere that's a popular tourist destination will have toilets somewhere. If you go somewhere genuinely remote (hard to in the UK), just go in a bush and cover it up or something.

In the UK they're called radar keys. I have one. I didn't mention it, 'cos I didn't think it was worth going to the trouble of getting a key for two weeks. Also, so many shops and restaurants don't even bother with locking their disabled toilets, so anyone can use them - key or no key.