Empty and on the ground near WWF Island House... Guessing some kind of wasp nest?

Yes it is,  from a paper wasp sub-family Polistinae. By the size of the large cells, I would say Polistes gigas.

I don't think so
For my experience，it is not P.gigas nest.
I think this is a P.sagittarius nest

Maybe, but the very irregular shape of the nest may not be that of P. sagitarius. Actually without having the nest in hand its very difficult to say. A paper wasp for sure

Thanks both very helpful
What is the etiquette around collecting an empty nest, is it OK?
This is great by the way http://insectahk.com/HK-Vespids.Rev.M%20Web.pdf
And looking to get this http://www.chinascientificbooks. ... f-hong-kong-p-6771/
Any recommendations for other references would be great

You can collect empty nests no problems (?) Well I can't see AFCD prosecuting you for it (if in country parks, CP's)) although theoretically you cannot substract anything from CP's, even if   dead.
When you collect a nest, try to locate where it came from (which plant/building) make a note of it, record date of collection, note the place name, a geographical coordinate is good and attach a label to the nest with these infos on it.
There are a lot of references available on WWW. From the reference sections of these papers/books you'll find more references....it's an expodential curve!
Thanks for your comments on the books