As current needs present an omni-faceted challenge to the current structures and priorities of societies, so a multi-faceted and holistic policy programme is needed to address them. This presents a substantial problem within the paradigm of academic work, which rightly tends towards the breakdown of complex systems into components that can be analysed more rigorously in isolation. The radical uncertainties introduced by the presentation of a programme that includes many discreet changes, many of which interact, leans against confidence that any specific finding, or even the entire edifice, withstands critique. Inevitably, inherent radical uncertainties pervade the exercise. Yet, it is precisely the responsibility to meet our inescapable obligation to address our long-term challenges that the academy is purposed for, so it is in alignment with that responsibility that this report is published.
Uncertainty is recognised throughout and, where the public data allows, mitigated by grounding each policy in it. Radical uncertainty, by contrast, is not something this report claims to remove.
Precision
Figures in this report are quoted to a consistent apparent precision, typically two decimal places of a billion, so that every table reconciles and every calculation can be reproduced and audited. That precision is a property of the arithmetic, not a claim about the world. Each model carries documented uncertainty: survey undercoverage and uprating assumptions in the tax models, behavioural ranges in the revenue estimates, demand and unit-cost assumptions in the service costings. These are stated in the relevant appendices, and in most cases the documented sensitivity band is wider than several units of the final printed digit. The meaningful outputs are therefore shape and ordering: which flows are large and which are small, the direction of distributional effects, and the existence of fiscal space at a scale that matters, not its second decimal. Where source ranges exist, the conservative end is selected. Published figures are not revised for movements smaller than their documented sensitivity bands; such movements are absorbed into the scheduled update cycle of this living document.