Data, sources and methodology
Every source this site uses, its cadence, licence and last-checked date — plus full methodology, the anti-fabrication rule, and the corrections policy.
The rule this site is built on
Every statistic on this site carries four things: the exact publication it came from, a link to it, the period it covers, and the date we retrieved it. Figures are parsed directly from official spreadsheets and APIs by scripts whose output is version-controlled — the history of every number is auditable. Where a figure can only be curated by hand (costs, inquiry findings, polling), it is stored with the verbatim sentence it came from. A figure that cannot be verified is either dropped or visibly badged as unverified — the build fails otherwise. We never invent, estimate or extrapolate numbers.
Source register
Small boat activity in the English Channel: Provisional operational data (daily arrivals since 2018; weekly French prevention estimates). The quarterly Illegal entry routes statistics are the authoritative series.
Immigration system statistics data tables (year ending March 2026): Asylum claims, backlog, support (incl. hotels and by local authority), returns, FNO returns, and the Illegal entry routes tables. Attachment vintages vary — each figure on this site carries the period parsed from its own table.
Offender management statistics quarterly (prison population by nationality): England and Wales. Prison nationality is not immigration status.
Safe and legal (humanitarian) routes + Resettlement by local authority (Immigration system statistics): Hum_01 route totals include in-country grants (mostly Ukraine-scheme extensions) — the out-of-country split is shown where arrival numbers are meant.
Immigration detention + Organised immigration crime summary tables (Immigration system statistics): Det_01 (entering/leaving/in detention) and OIC_01 (disruptions by threat level; recent quarters provisional).
Migration transparency data — Immigration Enforcement (FNOs living in the community): Table FNO_08a: foreign national offenders subject to deportation action living in the community (criteria and non-criteria basis from 2022 Q4).
Individuals referred to and supported through the Prevent Programme: Referrals are concerns raised, not offences. Ideology categories are the Home Office's own.
Census 2021 tables TS004 (country of birth) and TS029 (English proficiency): England and Wales only; census day 21 March 2021 — predates subsequent arrival waves.
NAO: Investigation into asylum accommodation: FY 2023-24 asylum support and hotel spending.
NAO: The Home Office's asylum accommodation contracts: AASC 10-year cost: £4.5bn original estimate vs £15.3bn current. Quotes reflect the NAO's published correction.
NAO: An analysis of the asylum system (HC 1517): FY 2024-25 asylum spending estimates.
National Audit on Group-based Child Sexual Exploitation and Abuse (Baroness Casey): Quoted verbatim with page references only.
IICSA: Child sexual exploitation by organised networks — investigation report: Quoted verbatim only (Part B.5, ethnicity data collection).
More in Common — published polling tables: Poll entries cite fieldwork dates, sample size and exact wording from the published weighted tables.
ONS A12: Employment, unemployment and economic inactivity by nationality and country of birth: Labour Force Survey estimates, not seasonally adjusted. ONS rate-limits automated access intermittently; on a failed refresh the previous quarter's figures are retained and dated, never approximated.
ICIBI inspection reports (asylum casework; contact with migrants without leave): The statutory inspectorate's findings, quoted verbatim with paragraph references.
Home Office annual report and accounts 2025-26: The department's audited accounts — losses and special payments disclosures quoted verbatim (p.223).
Methodology
Small boats (weekly). The Home Office publishes a time-series spreadsheet of daily small-boat arrivals since January 2018, updated weekly. Our script re-resolves the current file through the GOV.UK Content API each run (the file URL is date-stamped), reads the daily table, and computes annual totals, the year-to-date figure and the cumulative-by-day comparison. These are provisional operational data; the quarterly ‘Illegal entry routes’ tables are the authoritative series and are shown alongside.
Quarterly Home Office tables. Asylum claims, the backlog, support and accommodation (including by local authority), returns and foreign national offender returns are parsed from the official summary and detailed tables of the quarterly Immigration System Statistics. The tables on that page carry different vintages, so each figure's period is parsed from its own table's title — never assumed from the release date.
Prisons. The foreign-national prison population and its nationality breakdown come from the Ministry of Justice's quarterly prison-population tables (England and Wales). The share of the prison population is computed from the same table's own total — numerator and denominator from one source.
Periods. Home Office statistics mostly use years ending March; calendar-year series are labelled as such; financial-year cost figures are labelled FY. We render figures exactly as published and do not re-round.
Curated figures. There is no machine-readable government dataset for asylum costs, inquiry findings or polling. Those entries are curated by hand with the verbatim sentence from the source document, and the build rejects any curated figure without its quote.
Known limitations
- Small-boat weekly figures are provisional and revised; French prevention counts are operational estimates supplied by French authorities.
- Arrivals data counts detections — people arriving undetected, or clandestinely on larger vessels, are not in it.
- Nationality in arrivals data is as recorded at encounter and in some cases self-reported; age-assessment disputes exist.
- Prison nationality is not immigration status: ‘foreign national’ includes people living in the UK lawfully, and prison totals say nothing about irregular migrants by themselves.
- Census context is England and Wales only (Scotland and Northern Ireland ran separate censuses) and reflects March 2021.
- Local-authority accommodation counts are point-in-time snapshots; contingency sites open and close between quarters.
- Employment figures (ONS table A12) are Labour Force Survey estimates — small samples are volatile, and country of birth is not nationality. The workbook is a legacy binary file whose extraction needs a local Python step; if a refresh cannot reach it, the previous quarter's figures are retained and dated rather than approximated.
Corrections
If a figure here misquotes its source, email [email protected] with the page and the source document. Errors are corrected with a dated note on the affected page. Errors in the underlying official statistics should be reported to their publisher; we reflect published revisions at the next refresh.
Register last reviewed