I have a pair of Hot Tuna swimming shoes, size 11. Barely used; they were the wrong size for me.
A suggestion: if you normally wear size 11,then these will probably not be a good fit for you, particularly if you have narrow feet. My experience has been that, to fit well when swimming, they need to be slightly undersized. These would probably work best for someone who normally takes sizes 12 or 13.
Or, you could just try them anyway!
I'm in Islingword Street, near the Dover Castle.
William