from HK to London, by direct flight...aournd 12 hrs flight time! from 24Dec afternoon, until 26Dec, most of the shops will closed, even though the resturant also will closed!!! and on 25 and 26Dec, there will be NO public transport available, all the bus, rail, tube will all closed! So if you will rent a car by yourself, and won't go shopping, then it is still possible to go on that day, if not, you are better to leave HK on 26Dec or back to HK on 25Dec~