There's a discontinuous pattern re: reptiles in private hands and in zoos - broadly, UK zoos tend to either have species that are very common in private hands* or very rare. Species of moderate availability** in the pet trade tend not to turn up as much.
*As well as the good ol' Inland Bearded Dragon, I'm thinking of species like Hermann's Tortoise, Burmese Python, Leopard Gecko, Corn Snake etc
**like JR's House Snake, Sandfish Skink or Long-tailed Lizard
