Chinese Water dragon !!!
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When I saw this creature in the Princess of Wales Conservatory at Kew Gardens, I thought it was an Iguana. In fact it is a Chinese water dragon. ( physignathus cocincinus).
On the site of Kew gardens ( www.kew.org ) :
There are about nine water dragons that live and breed freely in Zone 1. They provide a natural means of controlling unwanted insects in the Princess of Wales Conservatory but tend to keep out of sight of visitors.