During the run-up to Budgets and other policy statements, we subject the Government’s draft costings of tax and spending measures to detailed challenge and scrutiny. We then state in the Economic and fiscal outlook and the Treasury’s costing documents whether we endorse the costings that the Government finally publishes as reasonable central estimates. Our approach to the costings process, including the roles of the Treasury and other relevant departments, and how we incorporate the impact of policy measures in our forecasts is described in Briefing Paper No.6: Policy costings and our forecast. We have also written a small number of working papers on evaluating costings and forestalling.
At each fiscal event, we produce an annex in the Economic and fiscal outlook on the announced policy measures since the previous event and an accompanying uncertainty ratings database where we assign each certified policy costing a subjective uncertainty rating. We also update our database of policy measures since 1970.