It may have changed heath 480, and I'm probably going back pre Covid when I was a member, but yes you could bring in non members and pay for them, I often took my gd swimming there on a Saturday and I remember paying and signing her in at the desk. So on hot days members would bring guests in Sometimes, I was told, those from other DL clubs without outdoor pools could use alternative clubs under their category of membership, they were allowed to do that. My club was outer London, where there 's a proliferation of DLs so nearby ones would be under 10 miles away, hence the crowding around the outdoor pool on a glorious day. Loved using outdoor pool in the winter, I do miss that, it was always warm, just had to brace myself for the getting out 
Hope you enjoy it Witzend, Heath is right, you need to use it often to get your money's worth.