From Green Belt to Grey Belt: evaluating the alignment of legacy assessment tools with the National Planning Policy Framework (2024) reform in England

The introduction of the ‘Grey Belt’ concept in the revised National Planning Policy Framework represents a significant shift in English planning policy, seeking to enable the development of lower contributing Green Belt land as part of the government’s response to housing pressures. Its implementation, however, relies partly on existing Green Belt Assessments prepared before the introduction of the Grey Belt definition. Although these assessments have supported both Green Belt protection and the identification of land for potential release through local plan reviews, they were not designed to apply the specific Grey Belt criteria introduced in 2024, particularly at the scale of individual development sites. Drawing on 18 planning appeal decisions and semi structured interviews with practitioners, this paper examines the extent to which the purposes, spatial units, and methodologies of existing assessments align with the new policy framework. Applying knowledge utilization theory, the findings show that methodologically compatible and spatially relevant assessments facilitate instrumental evidence use, whereas assessments based on unsuitable spatial units or reasoning that cannot be translated into the new criteria are more likely to be afforded limited weight or supplemented by site specific judgement. The paper concludes that clearer methodological guidance, regular evidence updates, and closer integration with plan making are required to improve consistency while retaining appropriate scope for contextual judgement.