Postern Gate Farm Newgate Street Village Hertford SG13 8QR Data via plota.co.uk

Green belt policy allows a short list of exceptions, such as limited extensions and replacement buildings. Anything else needs very special circumstances that clearly outweigh the harm.

Harm to a protected site is only accepted where there is no alternative and an overriding public interest.

Where development of farmland is needed, policy prefers poorer land over the best and most versatile (grades 1, 2 and 3a). Three sources: Natural England's post-1988 field surveys, which are definitive where they exist; the Defra predictive map for England (2025) and the Welsh Government predictive map, modelled from the soil map with 3a and 3b split; and the 1970s provisional map, which planners and other services still show, coarser and with grade 3 undivided. Where the provisional and predicted grades disagree, treat the predicted grade as the current estimate and expect an application to carry its own survey.

Sites of special scientific interest are the best wildlife and geological sites in the country. Development likely to harm one is rarely permitted.