Marwell has always held many 'park' species that are of no conservation value, although the majority of the collection is focused on rare species. The aspinall parks are similar, and while there are possibly fewer 'common' species at Howletts and Port Lympne, the collection you must surely albeit unknowingly be referring to as pioneering conservation in its truest form is Jersey Zoo, at least for the UK.
Yes I was thinking of Durrell as I believe he was the first (or at least one of the first) to realise the importance of captive breeding.
What I wrote was that neither are based "soley" on conservation of endangered species which is what cat-man wrote. Yes, both have made contributitions but each undoubtedly have other agendas as well.