Try private gym pools. My local council pool was terrible. I had different answers from different people and really rude staff but the gym are absolutely fine (if not pretty happy) about the fin as long as I'm sensible about taking up space during busy times and use the smaller fin if it is busier. However, it is a much smaller pool and it isn't very deep but I've been swimming in my local river all summer so I'm just glad to have somewhere warm that doesn't have a current. I think private gym pools can be much more accommodating if you are up for getting membership.