Hong Kong has lower taxes, but don't you pay double on your first year? And you may need "moving expenses"
Seriously though, stop it with the "rent in Hong Kong costs more than London" - not today it doesn't. Pre-2000/1999/whatever, that was certainly true, but now I see places in Hong Kong around £1000/month which would cost at least £1500 in a comparable "nice" central area of London. And it's a buyers market in Hong Kong, so bargaining with the landlord is a good way to knock a sizeable chunk off the rent - I saved a nice bit that way too.
I'm not saying Hong Kong's cheap though, as people earn comparitively less than southern English workers, but they do by and large have less to pay for too. But I know a few years ago HK had a crazy economy.