United Kingdom METHODOLOGY

The United Kingdom uses census ethnicity. White British - including the corresponding Scottish categories - and White Irish persons form the native population, while all other ethnic groups, including White Other, form the migrant population. In Northern Ireland, the available White category is treated as native. The definition can retain migration-related group distinctions across several generations.

The ethnicity model was selected because it is available across the UK censuses and includes later-generation group continuity that a foreign-born-only definition would omit.

The starting population combines the 2021 censuses for England and Wales and Northern Ireland with the 2022 Scottish census. England and Wales provide detailed ethnicity data by age and sex. Scottish age groups are distributed to individual ages. For Northern Ireland, minority shares from broader age groups are applied to the detailed population structure.

Fertility is differentiated by the mother's country of birth and applied to ethnicity-defined populations. The same age- and sex-specific mortality schedule is used for both groups.

Baseline migration uses the official long-term international migration series for 2015-2024 classified by nationality. Where the longer series does not provide a sex breakdown, the distribution observed in 2022-2024 is applied. The post-2020 movements remain part of the observed average.

• The model combines census ethnicity with fertility by country of birth and migration by nationality, the official variables available for the respective components.
• The starting population combines the 2021 censuses for England and Wales and Northern Ireland with the 2022 Scottish census.
• Northern Ireland's broader ethnicity age groups are aligned with its detailed population structure.
• Ethnicity is self-reported and can retain migration-related group distinctions across more generations than birthplace-based definitions.
• The observed 2015-2024 migration average includes the post-2020 movements recorded in the official series.

• Starting migrant share: 23.1%
• Baseline tipping point above 50%: 2053
• Reverse tipping point below 5%: 2095

• Office for National Statistics: Ethnic group by age and sex, Census 2021, accessed 28 May 2026.
• Scotland's Census and Northern Ireland Census 2021, accessed 28 May 2026.
• Office for National Statistics: Parents' country of birth, accessed 28 May 2026.
• Office for National Statistics: Long-term international migration, accessed 28 May 2026.
• Office for National Statistics: Single-year life tables, accessed 28 May 2026.