They used to be unheard of over here - for a long time the only British group was at Cotswold WP, and not even that was really on show, but with restricted viewing behind two windows with a corridor between in the quarantine building. First time I went to Cotswold, that was the reason - to see Yellow Mongoose for the first time in that weird 'exhibit'.
Now they've come to be really rather common - in at least 10 zoos in Britain and a total of 56 in Europe as per zootierliste.de. Very nice animals.
We don't do too badly for mongooses in Britain - Meerkat, Banded and Yellow in very good numbers, Dwarf and Cusimanse ticking over, and the odd Marsh still about. Not to mention the begining of a population of Narrow-striped (strictly a euplerid rather than a mongoose, but what the hey) at Jersey and Newquay.
I remember back in 2001/2 when Marwell was planning they're mongoose enclosure, and for a long time the intention was to keep ring-tailed mongoose, as apparentley some had become available in Germany and it would fit in with the Madagascan theme of the site (the enclosure is between the lemur and fossa complexes). Very unfortunately, none became available and at the last minute yellow mongooses were put in the enclosure. I do hope that Marwell can find a way to gain ring-tails for that enclosure in the future.