Just spoke to Lou at Eastcoast Stand Up Paddle. He has some that are dedicated to SUP and have either ankle or calf option. Just ordered two of the ankle ones
Naish make a coil-leash for racing. For the surf, we've been using Crowe Hayley handmade in the US big-wave 8mm surfleashes. They are hand-tied so can be re-used if broken and so far no problems........
Thank you to everyone... Following your suggestion I contacted Ocean & Earth and ordered their dedicated SUP leash for my school and for the shop. I will let you know when they will arrive (should be soon as their service is very fast! Amazing).
Bye Jankie
PS. Coil leash for big waves I don't think are the right call but for Race/Down wind seems like the logical choice