An undertaking of this magnitude had to be tackled collectively, and involved the close co-operation of Conservation and Research staff of the Nature Conservancy, the former organised into regional groups with responsibility limited geographically but covering all habitats, and the latter organised into habitat survey teams with responsibility limited ecologically but covering the whole country. For each Region an inventory was compiled of all sites with noteworthy conservation value, arranged in grades of importance. This involved tapping as many sources of information as possible, both within and outside the Conservancy, literature search, and the organisation of field survey. In the South Region of England a complete survey of all semi-natural ecosystems has been made, the conservation value of each site mapped at the scale of 1: 25000 and more detailed descriptions and records made for the most valuable sites. This ideal of complete coverage has not been achieved in other Regions, some of which have very large areas of semi- natural vegetation and thus present much more difficult problems for basic survey.

The habitat survey teams were provided by regional staff with the lists of the most important regional sites including existing NNRs, other categories of nature reserve, Sites of Special Scientific Interest, and unscheduled, recently discovered sites which appeared to be of a high quality. The habitat survey teams examined the most important sites, assessed their relative merits on the national scale and prepared recommendations for a final series of key sites for each habitat. In practice, regional staff and habitat teams worked in close conjunction, and were often involved in field survey at the same time. Habitat teams frequently undertook initial field survey to locate sites of importance in little known districts.

Such surveys were based on information about sites of known or suspected interest and on examination of 1 in. and 2 in. Ordnance Survey maps. Knowledge of the range of variation of ecosystems within each region, in relation to that present on scheduled sites, focussed attention on filling obvious gaps in the representation of habitats. The surveys often involved prospecting, that is, examining areas of country more or less systematically to locate sites of interest and then making a more careful study of them. Student assistance was widely used in this field survey, especially in recording sites of known interest.

Both groups collected records of essential biological and environmental data for the more important sites, using prepared record cards and check sheets for convenience and uniformity in presenting data on location and size of site, physical features, climate, geology and soils, land-use, vegetation types, flora, fauna, and features of special ecological or biological interest. The Biological Records Centre at Monks Wood Experimental Station supplied record cards, or helped in their preparation, provided existing information on sites and ecosystem features, including species distribution, and processed and stored the recorded data.

Information on sites and ecosystem features has been gathered from a large number of professional and amateur biologists and other scientists outside the Conservancy. A considerable effort has been made to seek the advice and information of all individuals and bodies concerned with nature conservation, and in a position to help the Review. Non-statutory reserves established by other nature conservation bodies, notably the Royal Society for the Protection of Birds, Society for the Promotion of Nature Reserves, the National Trust and local Naturalists' Trusts, have been taken into account.

A Scientific Assessor, D. A. Ratcliffe, was appointed to the Review, to supervise and assist with various operations. His functions have been to assist in defining a descriptive framework of reference for ecosystem variation; to advise on field methodology and to formulate a rationale for the assessment of nature conservation value of sites and the needs for representation within a national key series; to help identify gaps in the existing NNR series; to approve key site selections, adjudicating when there was disagreement or doubt about the value of sites; and to compile and edit the final report.