Because of problems experienced by dwellers of such flats, in 2003 a new Building Regulation (called Part E) was introduced. This sets minimum stds for soundproffing between adjacent dwellings. There are different stds for new flats and refurbishments. Developers have to demonstrate they either meet the std by organisaing a test, or they have to use what is known as a compliant solution (one that is designed and pre-tested to meet the std). There is no retrospective application of this std - just look out for when your chosen flat was built!