Sex harmonisation guidance

The Government Statistical Service (GSS) Harmonisation team is currently working to develop new sex data harmonised guidance and standards, in line with the GSS Harmonisation workplan published in December 2024 and last updated in May 2026.

This update sets out our activities and what will happen next to publish harmonised guidance and standards for collecting data on sex, which we expect to do in Summer 2026. We are also working to produce guidance and standards for collecting data on gender identity, and you can learn more about this on the gender identity harmonisation guidance webpage.

For more information or advice on this topic, please contact Harmonisation@statistics.gov.uk.

The sex harmonisation guidance page was published prior to the April 2025 UK Supreme Court judgement on the meaning of sex for the purposes of the Equality Act 2010. There is not currently a harmonised standard for collecting data on sex. The previously published guidance set out how sex was included in the Census 2021 in England and Wales and Scotland’s Census 2022. This harmonised standard guidance page will be updated with new guidance and standards in Summer 2026.

Next steps to develop a harmonised standard

The GSS Harmonisation team recognises the importance of evidence-based harmonised standards for data collection on sex. Statistical producers and others who use the harmonised standards need to be sure that the questions and associated respondent guidance are suitable for the purposes for which they are collecting data. Official guidance and legislation for data collectors to consider when determining what their data needs on this topic are, include the:

• Equality Act 2010 (which legally protects people from discrimination in the workplace and in wider society based on sex, among other protected characteristics)
• Gender Recognition Act 2004 (which enables people to change their legally recognised sex by obtaining a Gender Recognition Certificate, or GRC)

In April 2025, the UK Supreme Court ruled that sex, for the purposes of the Equality Act, refers to biological sex unmodified by a GRC. This means that sex-based protections under the Equality Act must be based on biological sex, that is, the sex of a person at birth. We use the term ‘certificated sex’ to mean a person’s sex at birth or as modified by a GRC.

User needs research identified a requirement for the harmonised standard for sex to support statistical producers currently collecting data on sex and those considering whether and how to make changes to data collection on sex. We are prioritising testing for a harmonised standard which supports data collection for:

1. Biological sex (sex at birth)
   and
2. Certificated sex (sex at birth or as modified by GRC)

This work has been accelerated, reflecting the urgent user need for statistical guidance shared with us by official statistics producers. We are currently undertaking cognitive and usability testing with participants of diverse backgrounds and characteristics to ensure that question wording and associated respondent guidance are easily understood and correctly interpreted. This testing ensures a rigorous evidence base for our new recommended standard, which we will publish in Summer 2026.

We recognise that user needs and the context for official data collection continues to evolve, and therefore our guidance may need to change further after this date as circumstances change.

We are continuing with our workplan for gender identity. This work may also affect our future guidance, for example if additional advice is needed for statistical producers intending to present both sex and gender identity questions in the same data collection instrument.

We will also continue to research other topics related to sex, such as variations in sex characteristics (VSC, sometimes referred to as intersex, or differences of sex development).

Considerations for data collection ahead of new harmonised standard

The Office for Statistics Regulation (OSR) has provided guidance to support official statistics producers in applying the principles of the Code of Practice for Statistics when making decisions about the collection and reporting of statistics and data about sex and gender identity. This includes the importance of ensuring that data and terminology on these topics are clearly explained and not used interchangeably.

The OSR guidance includes a section on questions for statistics producers to consider, which includes the following questions for data collectors planning to report on sex:

• Do you have a clear reason to collect information on sex?
• Are you clear on how you are defining sex?
• Does your definition of sex meet the needs of the different users of your statistics?
• Do you understand what data you can, or should, collect about an individual’s sex to comply with relevant legislation?

If you are looking to introduce or amend a sex question in your data collection, where possible, we would recommend waiting for our work to develop new harmonised standards to conclude this summer.

We are aware that many users of statistics are currently using a question consistent with Census 2021 in England and Wales. It is important to be clear that guidance for the Census 2021 sex question in England and Wales reflects the definition of ‘sex’ for the purposes of the Census Act 1920 (as it applies in England and Wales), as agreed in a consent order made by the High Court in 2021. The guidance stated: “If you are considering how to answer, use the sex recorded on your birth certificate or Gender Recognition Certificate”, directing respondents towards providing “certificated sex” as previously defined.