You need far more than just a UK address. Even with a UK address, you need someone to wait to receive the delivery from the Bookpeople. Then, to help to deliver it to HK for you.
There is extra people and delivery cost involved. Depending on the weight and size of the package, it may cost you more than the books. Last Christmas, I ordered GBP50+ books from theBookPeople and spent more than GBP70 in delivery with the help from a colleague in UK.
The above logistics involves money and better be handled by someone you trust (assuming he/she trusts you too). I'm afraid this request can hardly be satisfied in a public forum.
Are you okay to take the risk for having a free ride with a stranger? If a kind and helpful EK member told you he/she will order it and can help you but needs an upfront deposit of GBP60 from you, will you pay?
This will work within the group of people with mutual trust. Why don't you bring it up with the parents of your child's classmates? It will incur less risk and admin. overhead than doing it here.