The National Vegetation Classification (NVC) is one of the key common standards developed for the country nature conservation agencies. The original project aimed to produce a comprehensive classification and description of the plant communities of Britain, each systematically named and arranged and with standardised descriptions for each.It was originally commissioned in 1975 by the Nature Conservancy Council (NCC) and was intended as a new classification, not an attempt to fit British plant communities into some existing scheme derived from elsewhere in Europe. The general approach adopted was phytosociological and, therefore, concentrated on the rigorous recording of floristic data. It did, nevertheless, try to avoid over-scrupulous selection of samples, rejection of awkward data and preoccupation with the hierarchical taxonomy of vegetation types. (text from JNCC NVC page)More about the methodology on the JNCC website.