Designer bags above £500

Hello,

I will be flying to Shanghai via Hong Kong in a few days, would like to check if I must declare any designer bags purchased while in China please? In particular, I would like to buy one from Givenchy (~£895) and one from Louis Vuitton (£2k+).

If bought in China I assume I need to declare and pay tax? And also, would it be cheaper to have it shipped to me from a relative in the UK? Not sure if any declarations would need to be made in that instance, if I need to pay tax when bringing it out etc.

Any help much appreciated