Guidance

Business Critical Models in the Ministry of Defence in 2025

Published 17 November 2025

1. We are publishing a revised list of the MOD’s business critical models^{[footnote 1]} as of April 2025 as part of our response to the Macpherson Review of Quality Assurance of Analytical Models. We have continued to regularly update and publish a list of the Department’s business critical models on our website. The list is expected to change over time as existing models are revised or retired and new models added. The list that has been published represents the most up-to-date version and supersedes any previously published lists.

Background

2. Sir Nick Macpherson, the then Permanent Secretary at the Treasury, carried out a review of the quality assurance of analytical models that inform policy across government. The review was published in March 2013 and made a number of recommendations, including encouraging departments to publish a list of their business-critical models: Review of quality assurance of government models.

3. As a consequence of the review, Government produced guidance on how to produce robust, fit for purpose analysis  in the Aqua Book This has recently been updated. The 2025 list of models was prepared before publication of the new edition of the Aqua Book in July 2025 and so is based on criteria to identify business-critical models previously used in Defence. We do not, however, expect that the new Aqua Book would have changed which models are identified as business-critical. No MOD list was published in 2024.

How have we implemented the Macpherson Review?

4. As required by the Macpherson Review, our governance statement must confirm that we have an appropriate quality assurance framework for analytical models. This statement is published in the Department’s Annual Report and Accounts. We also ask each Arm’s Length Body that has one or more business critical models to confirm their arrangements are appropriate in their annual Assurance Statement.

5. Other steps that we have taken to instil a culture of analytical assurance in MOD include:

• embedded quality assurance of analytical models into the Standards workstream of the Department’s Analysis Function and have now published guidance which is available across the Department.
• over time we have expanded our coverage of models across Defence, primarily by growing the network of analysts through our Quality Assurance Working Group.
• continued to promote transparency by publishing a list of our business-critical models. Changes reflect the churn of models in Defence, with some being retired and other new models coming into service.
• promoted a pro-quality assurance culture, for example by using Modelling Champions in key organisations and, where appropriate, including quality assurance as a work objective for staff.

1. As suggested by the Macpherson Review, we define a model as business critical if it drives key financial and funding decisions, it is essential to the achievement of our business plan, or if error could lead to serious financial, legal or reputational damage. ↩