Aescalapian snake, not too distantly related to native grass snake. Can only be considered Britain's rarest snake if you likewise consider Black rats the nation's most endangered mammal.
I too had heard about Crumple the elephant escaping, but it could have been through the rumour mill that is Zoo Chat! The 'escape' may not have been from the exhibit, rather she could have made a dash for it while being walked (although it would be difficult with leg chains). Escapes are not usually advertised by zoos, unless of course it is too difficult to hide the facts. I remember a lemur getting out of it's enclosure, and while there was a large crowd surrounding us while we recaptured it, nothing was leaked to the press. Just entertainment for the masses on the day...