NESO releases six PwC reviews of its spatial energy plan, and the model was out of scope

Serguey Asael Shinder11 October 2026, 09:392 min read

Britain's National Energy System Operator answered information request FOI-26-208 on 8 October by publishing six PwC reports on the assurance of the Strategic Spatial Energy Plan (SSEP) — the plan meant to say where new generation, storage and networks should go. The requester had asked how the value of natural capital enters spatial planning; NESO narrowed the request, with the requester's agreement, to PwC's work on the SSEP and on its alignment with HM Treasury's Green Book, and handled it under the Environmental Information Regulations.

What was released. The response letter lists: an SSEP methodology review (final, 30 May 2025); an extract of a gap analysis and roadmap (June 2025); a programme management review (June 2025); two action reports from PwC's reviews of the SSEP approach and of its data controls (final, June 2026); and an assurance framework review (final, July 2026). Names and job titles of NESO staff are redacted. Three drafts are withheld as unfinished documents, among them a review of the SSEP Pathway Options Report dated August 2026, of which, NESO says, no final version existed when the request arrived.

What PwC asks NESO to fix. The data-controls report groups its actions into four themes:

• Inputs from the energy department (DESNZ): obtain transparency on how DESNZ produces its input data and assumptions, and formalise who owns them, so that versions can be traced and NESO can answer outside scrutiny.
• Documentation: keep a formal trail showing how DESNZ data was validated and used, and merge risk tracking between the Economic Modelling Inputs Database and the Assumptions Log into one view.
• Assumptions governance: give every assumption an approver and a review date, set approval requirements by risk and impact, and add an extra layer of internal review for high-risk ones.
• Modelling QA: more automated checks, spot-checks of samples alongside high-level validation, updated operating procedures that match what the team actually does, and named owners for key controls.

What the reviews did not look at. The reports state their limits plainly. PwC did not review the inputs, algorithms, calculations or outputs of the Plexos model that produces the pathways, did not formally assess compliance with the Green Book, and did not verify that actions were completed — where an action is marked Complete, that is NESO's own assessment. PwC also notes that it did not establish the reliability of the NESO sources it used.

Why it matters. The SSEP is meant to guide where the energy system is built. The released documents show a programme being told to make its assumptions traceable and owned — the kind of finding that is cheaper to act on before a plan is published than after. They do not show anyone outside NESO checking the numbers the model produces. Readers who rely on SSEP outputs should keep that distinction in view: the assurance so far is about process, not results.

Source: NESO, FOI-26-208, External assurance for SSEP, response dated 8 October 2026 — https://www.neso.energy/foi-26-208-external-assurance-ssep-8-october-2026