“BREEAM is the Building Research Establishment Environmental Assessment Method for buildings. It sets the standard for best practice in sustainable design and has become the de facto measure used to describe a building’s environmental performance.”
These days sustainability is the term around which the entire planning system dances.  This was finally set in stone by the enactment of the National Planning Policy Framework which presumes consent for “sustainable…” (if of course the word can be properly defined and applied!).
Planning applications speak of reaching Code 4, or whatever to measure levels of sustainability.  They are referring to the Code for Sustainable Homes.  This is the future.  This is the BREEAM website with which it is wise to become familiar.