The HM Treasury Green Book is the main document setting out Government guidance on the appraisal of public investments.
The purpose of this guidance is to ensure that policies, programs and projects adopted are the best ways to achieve policy objectives and make the best use of public resources. The guidance covers all stages of the appraisal and evaluation cycle.
According to this guidance, business cases should be structured into 5 separate cases: Strategic, Economic, Commercial, Financial and Management. A checklist for assessing Business Cases is available here.
The HMT Green Book includes guidance on how to discount benefits and costs to obtain the value for money of an investment and how to account for risk and uncertainty in appraisal.
In addition to the main guidance document, the Green Book includes additional documents as supplementary guidance. These are available here. These include specific chapters on topics such as “optimism bias”, environmental impacts, and transport.