Wow, thanks guys....
My local chinatown's travel agent went bust a few years ago so I don't have a local one to see.
Looked at Air New Zealand, if i leave in Sept and come back to UK for xmas (i.e. a return flight) it's 566 altogether but if I get a single to HK for Sept (same date and same flight as the outbound return jouney) it's 679!!!!! It really doesn't make sense!