In reply to your question ''Is there anywhere to walk or sunbathe naked in or around Bristol?'' the answer is yes!
I've posted an article about Whale Wharf, an stretch of coast near Littleton on Severn (near Thornbury) that is perfect for nudists. You can sunbathe there, as I and girlfriends have done for several years and it is a great place to walk nude. I've walked naked from ny car on many occasions, solo and wth friends - if I'm really daring I'll leave my clothes in the car so as not to be bothered with carrying anything.
Perhaps we can meet there next summer?