I’d definitely go along to the tri training sessions. I go to a masters session up here in Sheffield and there’s a real mixed ability split in to lanes so you don’t feel out of your depth with some swimmers tearing past you. Really good way to learn drills too.

I started by getting a couple of one hour sessions with a swim instructor who started from scratch. I couldn’t do more than a few lengths crawl without passing out. Ended up focusing on swim smooth approach which worked wonders for me. Whilst I’ve now lapsed on fitness with a bit of training you should be able to get sub 30 minutes open water mile pace.