1. Higher APD compared with 2010.
2. When did you book your tickets last year ? I ask, because airlines (especially non-stop carriers) tend to offer lower seat sale rates nearer the time depending on demand.
3. Airlines have cut capacity on the HKG route. Fewer seats mean higher fares.
4. Although Britons may not be travelling as much, other nationals are thanks to strong currencies, rising prosperity and so on.
5. Last but not least, you are travelling at some of the busiest times of the year.
For a better price:
1. Wait until nearer the time (but then you may not get the dates of your choice).
2. Book an indirect carrier.
3. Travel midweek.