Fit for policy? Some evidence on the application of development viability models in the United Kingdom planning system

This paper investigates the application and use of development viability models in the formation of planning policies in the United Kingdom (UK). Particular attention is paid to three key areas: the assumed development scheme in development viability models, the use of forecasts and the debate concerning Threshold Land Value. The empirical section reports on the results of an interview survey involving the main producers of development viability models and appraisals. It is concluded that, although development viability models have intrinsic limitation associated with model composition and input uncertainties, the most significant limitation is related to the ways in which they have been adapted for use in the planning system. In addition, it is suggested that the contested nature of Threshold Land Value is an example of calculative practices providing a facade of technocratic rationality in the planning system.