I think they've declined in the UK in recent years though. Places like Edinburgh and Marwell used to have them but not for a very long time now. I think they could die out at Whipsnade soon and even Howletts don't have very many. West Midlands seems to have a viable group though.
I thought I still saw a few either in 2008 or 2009 but I noticed it was only females. Maybe it was an earlier visit though.
From ISIS; Knowsley 26, West Midlands 16, Port Lympne 1. Whipsnade & Howletts/Bekesbourne aren't mentioned, so I think Whipsnade no longer have them, but evidently Howletts still do.