laundromats in Cornwall or Southern England?

There are laundromats there, do a google search of places you will be in or towns/villages close by.

Thank you, I will try that!

outside of big cities they are actually quite rare. try Yellow Pages online at https://www.yell.com/ and search for "laundrettes". Then make sure the results don't include laundry services (which is someone who takes your laundry and does it for you) and change the search order to Distance. My town has a population of 90,000 and a university with a couple thousand students - it has ONE launderette.

It's unusual, though not unknown, for a laundrette to also sell washing powder or liquid so you might end up lugging a load around with you.

If you are staying in a B&B or other smaller owner operated lodging you can ask to do a small load for a gratuity. I often just hang everything up overnight to air out if not soiled. Microfiber things will dry overnight if hung on line. If you are near a town there will be laundromats. Some campgrounds even have laundromats.

Or do what Brits would do and bring enough clothes for 2 weeks! You are on holiday - life's too short to be washing on holiday!

There are far fewer launderettes than 20 years ago, due to a lack of demand. Even most students have a washing machine at home!

If you stayed in an apartment part way through, take one with a washing machine.

Launderettes
http://www.bbc.com/news/magazine-10957093

https://www.yell.com/s/launderettes-bristol.html
https://www.yell.com/biz/laundrette-moreton-in-marsh-1395301/#view=map

Interestingly a launderette just opened up just round the corner from my parents' house - catering mainly for service washes for those who don't have the time to do their own, rather than not have a machine, although there are still a few doing their own in the evening.