Impact of UK Supreme Court judgement on Office for National Statistics work

FOI reference: FOI-2025-3098

The attachment was updated on 8 January 2026 as the wrong file had been uploaded in error.

You asked

Following For Women Scotland [2022] UKSC 31 and [2024] UKSC 12, references to "sex" in the Equality Act 2010 are to biological sex. This directly concerns ONS classifications, harmonised variables, EIAs and methodological guidance where sex is a determinant of life expectancy, healthy-life, labour market, pensions and migration statistics used across government.

Please disclose all recorded information held by ONS from 1 January 2023 to the present relating to:

1) Legal compliance, methodology & EIAs

• Legal advice (internal/external), governance or risk papers on ONS obligations post-UKSC; any reviews/changes to definitions of sex vs gender identity (including harmonised standards, questionnaire design, coding frames, metadata, microdata access policies, and any OSR/UKSA Code of Practice compliance assessments).

• Training materials, slide decks, workshops or staff guidance issued on sex/gender variables, and any decisions/justifications where gender identity was used in place of sex.

• Equality Impact Assessments, DPIAs and internal fairness/legal reviews where sex classification affects labour force, pensions/SPA, healthy-life expectancy, migration, housing and health statistics.

• Version histories/change logs showing when and why definitions/questions/metadata were altered following the UKSC rulings.

2) Safeguarding & immigration/resource-impact relevance

• Assessments/briefings about safeguarding implications of substituting gender identity for sex in statistics relevant to healthcare, prisons, education or social care.

• Material on how migration statistics interact with NHS capacity, housing and local-authority provision; any references to eligibility/verification (HC2/HC3, NRPF, right-to-work) insofar as they bear on interpretation or quality of statistics.

• Any reviews of fraud/abuse or misclassification risks linked to visa categories or administrative sources used by ONS; data linkage or undercount risks affecting resource allocation.

3) Public spending, corrections & quality management

• Analyses of the financial/legal/reputational risks of statistics inconsistent with the UKSC definition; DQMI/quality reports, methodology approval/assurance notes, change-control logs, revisions/withdrawals/annotations made as a result; external communications plans and stakeholder notices.

• Any OSR casework or regulatory correspondence on sex/gender classification, including concerns, assessments, or outcomes.

4) Triangulation & devolved impacts

• Correspondence/briefings between ONS and UKSA/OSR, HMT, DWP, DHSC, Home Office/MAC, DLUHC, and devolved administrations (incl. Scottish Government Chief Statistician and National Records of Scotland) on sex definitions in datasets; impacts on pensions, migration, health and housing; distributional or budgetary effects for Scotland, Wales or Northern Ireland.

• Records comparing or reconciling ONS outputs with named datasets where sex classification is material (e.g., Census 2021, Labour Force Survey/APS, Opinions & Lifestyle Survey, Crime Survey for England & Wales, International Passenger Survey, ONS Longitudinal Study, linked admin sources from HMRC/DWP/NHS).

5) Transparency, impartiality & external influence

• Records of consultation with or payments to external advocacy/lobby groups (e.g., Stonewall, EDI consultancies, migrant NGOs, business lobby groups) on definitions, questionnaires or methodology concerning sex/gender variables, including contract numbers, values and deliverables.

• Minutes/correspondence on impartiality (Nolan Principles), conflicts, or decisions to amend/withdraw ONS outputs because of the UKSC rulings.

• Communications with ministers/SPADs/lobby groups regarding census/ONS outputs relevant to sex, gender identity, immigration or equality policy.

6) Names & accountability

• Names and roles of ONS officials/statisticians/consultants acting in their official capacity concerning the above (senior responsibility owners, approvers, and project leads).

We said

Thank you for your request.  

As your request is centred on the Supreme Court judgement on the meaning of "sex" in the Equality Act 2010 published on 16 April 2025, we have interpreted your individual questions to be in relation to this judgement.   

Data collected and published by the ONS prior to the Supreme Court Ruling cannot be retrospectively changed as it would not be possible to change the basis on which those data were collected and defined. Similarly, ONS methodology materials describing work carried out would not be updated where they provide an accurate historic record, which is important for transparency of our data. In addition to the material provided in response to your FOI request, in May 2025 the National Statistician provided an answer to a written parliamentary question on Census 2021 data and the Supreme Court judgment that might be of interest. 

As set out in the Government Statistical Service (GSS) Harmonisation webpages, the creation of harmonised standards on sex and gender identity is one of the priority areas of harmonisation work. This work will take account of recent official publications and developments. The UK Supreme Court judgment is one of those developments.  We are awaiting publication of a new Code of Practice for services, public functions and associations from the Equality and Human Rights Commission. Information from these and other sources, will help us to understand user need for data on sex to inform the development of harmonised standards and guidance. The new standards will be developed through rigorous research and testing with a range of users.  

While the GSS Harmonisation review is taking place there is therefore minimal material of the type you have requested about the definition of sex, correspondence, guidance, or reviews around changes to definitions. An update on the activities of the Harmonisation team will be published in the new year. 

In parallel, the ONS is currently consulting on user needs for Census data via the ongoing Census 2031 Topic Consultation. The ONS invites respondent views on how sex data are used and the impact these uses have. Development of Census plans and materials will follow once clear user needs have been established. 

Please see the associated download containing the information we hold in scope of your request. Please note, regarding the comments that have been made on the Census Topic Consultation, we have now published the document on the ONS website. 

Personal data of those below Director level has been redacted under s.40(2) of the Freedom of Information Act 2000 (FOIA).

Some further minor redactions have been made to page 4 of the release. This is information was communicated to the ONS by a third party with the expectation of confidence and also contains legal advice subject to legal advice privilege. This information is therefore withheld under s.41(1) and s.42(1) of FOIA. Whilst we acknowledge that there are transparency arguments in favour of disclosure to help to understand the organisation's position following the SC Judgement, we feel this has been fulfilled by the information already disclosed, which evidences the approach taken following the judgement. Furthermore, the inherent public interest in the need to safeguard the full and frank discussions between organisations and their legal advisors is strong. The public interest test falls in favour of withholding this information in this case.

You asked for information on names and roles of ONS individuals – information on our Senior Leadership Team can be found on our website. Information on Board and Committee members can be found on the UK Statistics Authority website.