Well a couple suggestions:
1. Put Bufo bufo under the toad heading instead of the frog heading.
2. A compatibillity chart would be quite useful, I mean you don't want some one going on your site and then mixing an axolotl with many of the smaller aquatic species, and ending up with huge losses. Also you should make it clear that mixing animals from different continents is not advisable.
3. Though I am not completely sure, I have a feeling that there are many american and asian species which would be fine (not mixed with european species of course) in England's climate that have not included in the species list. I can think of only two right now which happen to be particularly invasive species: red eared terrapins, and american bullfrogs.
4. Some people here keep axolotls in out door ponds, they won't run away.
Well I hope I have helped you.