What I find is that a lot is so-called "luxury" new residential blocks in London (often high rises) have pretty much no sound insulation between flats, which for a modern construction is shocking, let alone a luxury building. I am not convinced that upmarket constructions give you any guarantee of build quality. In fact many of these luxury flats were sold off-plan in Asia to people to whom it was a financial investment and had no intention to ever live there, I can see why the developers wouldn't bother.