Add Baytree, Bug Parc, Hunstanton Sea Life Centre, Watatunga, Pensthorpe, Ark and Lincolnshire Wildlife Park- the East is swimming in zoos lolIf purely looking to add additions to your life list of collections visited I would suggest that East Coast might be a good idea. Amazona Zoo, Banham Zoo, Africa Alive, Thrigby, Colchester, Jimmy's Farm etc.
Also easy to strike in coast also for Hamerton, Linton, Shepreth, Johnson's of Oldhurst etc.
If looking for the "best" zoos however, then the South West is hard to beat for reasons others have explained. But i suspect you may be based that way anyway from your posting history.
I think the West Midlands is one of the best areas, as you’ve got Dudley, BWCP and the UK’s only sea otters in Birmingham, WMSP and Twycross very close by, then Chester and Peak Wildlife Park are pretty easy to get to as well (assuming the trains are running).Uncertain about your preferred distance for driving. The Midlands area is a suitable option. You could visit Dudley Zoo, Birmingham Wildlife Park (though it's quite small), and then proceed to Bristol Wildlife Project, Twycross Zoo, and Chester Zoo. The simplest approach is to open Google Maps, search for zoos, and get a visual representation of the distances available. Then, you can pick where you want to stay.
It’s a little further afield but you could also add Knowsley Safari Park to that list tooI think the West Midlands is one of the best areas, as you’ve got Dudley, BWCP and the UK’s only sea otters in Birmingham, WMSP and Twycross very close by, then Chester and Peak Wildlife Park are pretty easy to get to as well (assuming the trains are running).