Yes, have to use a courier and it's so expensive! Cheapest quote I've got so far is £100 for 1 25kg box which is crazy when we sent 27 boxes of belongs when we moved here for £400!
Oh ok. My mum tried to post us some stuff surface mail a couple of years ago and was told by the post office that that service wasn't available anymore.
If that's not actually true that's quite annoying!
It looks like your mum was given incorrect information. Parcelforce ship boxes of up to 30kg by surface to HK. Perhaps some people get confused because it's Parcelforce rather than Royal Mail but Parcelforce are actually part of the Royal Mail Group.