Gatwick zoo was a small collection with the appearance of a bird garden, with aviaries, enclosures and a small lake set in front of a small mansion. Most of the bird species were available in private aviculture at the time, though not necessarily common in zoos. I believe they had sunbirds for a while in the entrance exhibit. The most interesting enclosure was the mixing of spider monkey and squirrel monkeys on a large island, with a mature living tree in the centre which they could climb. Both were fairly large groups, seemed compatible, and were breeding.
Gatwick was the recipient of some of the 'dowries' paid by Windsor Safari Park's receivers on its closure for rehoming various species. I believe Gatwick received Windsor's penguins to join their own small group, as well as possibly flamingos, again to join their own, and pelicans (which they had not previously kept AFAIK). There may have been other species too. From the money they received, Gatwick were able to build several new themed exhibits - such as a desert beach habitat for the penguins, and possibly new enclosures for their existing meerkats and otters, which were the first such exhibits in a garden of aviaries and very simple enclosures. The David Taylor book on Windsor's closure is my source for this.
When Gatwick closed, I believe the white-throated capuchins and spider monkeys went to Chessington. I think the remainder/descendents of the spider monkey group are still at Chessington today.
Gatwick seemed very much someone's private hobby that happened to be open to the public. I rarely saw contributions in IZN or other publications so am unsure whether they had notable success in the breeding or husbandry of any of the species they held.
The gallery on this site has a few photos, others are to be found here:
Gatwick Zoo August 2002