@KevinB Of the four countries of the United Kingdom, Edinburgh Zoo, Belfast Zoo, Birdland, Folly Farm, Blackpool Zoo and Whipsnade Zoo all keep (Sub-) Antarctic penguins in outdoor enclosures, but also SeaLife Birmingham, SeaLife London and The Deep (3 Aquariums) hold theirs in indoor enclosures. I don't know of any specific reason for keeping them outdoors, perhaps the generally cooler climate (however after the temperatures this week, that certainly isn't true!) but some of the zoos who keep their penguins outdoors do have decent breeding records with the species.