If you mean building regulation E (equates to a fairly reasonable standard of acoustic privacy) I think this became compulsory for works starting after April 2005, so plenty of recently completed stuff and even some stuff still in the pipeline is not compliant.
Plenty of flats built in the last 40 years have only a partition wall seperating them, but it's not necessarily true that this is worse than older, "more solid" builds. A single course of bricks seperating one demise from another can let more noise through than acoustic plasterboard and resilient bars. The worst offenders (and the cheapest to build) are those which just have two sheets of standard plasterboard either side of a void seperating the flats. You can look forward to hearing the neighbours flush the loo and pry into the details of their most intimate conversations, a situation which reg E tries to end.
The walls may be one thing, but after renting numerous types of flats in London over a number of years I've come to the conclusion that what happens above the ceiling is the most critical of all to ensuring a good night's sleep. The worst offenders are unsealed (and, in modern fashion, exposed) floorboards supported by the same joists hanging the plasterboard ceiling. However, even sealed concrete floors will happily conduct impact noise, and non-impact noise invariably finds a way down through service ducts. Effective solutions to this pernicious problem:
1) control the space above your bedroom (i.e. it's part of your flat)
2) ensure the space above is empty (i.e. top floor flat).
3) live on a very busy road
4) go deaf