Many expats assigned to Hong Kong are given an expat package. What this entails is subject to much debate AFTER people get them (because they generally don't know what they need until it is too late). With that, here are some suggestions for things you should negotiate BEFORE you leave:
1) Moving Expenses. Do they pay shipping or give you cash (and you shop for the cheapest and keep the rest)
2) Moving Expenses II. Do they give you a small amount to replace certain items, like tin openers, placemats, etc that you forgot
3) Housing Allowance. How much will they give you per month to help with housing
4) Tax Equalization. Will they provide money to assist you in filing taxes and/or ensure you don't pay more than you would working in the UK (complicated).
5) Health Insurance.
6) Education Assistance. Do you have kids? You'll want them to go to one of the (few) expat schools
7) Airline Tickets--Emergency. They should buy you a ticket for an emergency trip home to care for a loved one
8) Airline Tickets--Personal. 1 or 2 tickets a year to come home and relax
9) A driver. If you are going to have a car (few do) than why not have a driver?
That's a good place to start.
From the company's standpoint, you are working in Hong Kong just as if you were working Cambridge or Newcastle--no big difference. But from your standpoint, you know it is a big difference and you shouldn't lose money going off to do the company's work in another country.