ONS coding system
code used in the United Kingdom for tabulating statistical data
The ONS coding system was a hierarchical code used in the United Kingdom for tabulating census and other statistical data. ONS refers to the Office for National Statistics.
It was replaced by the GSS coding system on 1 January 2011.
Code formulation
Principal authorities
The code was constructed top down from a four character code representing a unitary authority or two-tier county and district.
Electoral wards and output areas
Local government wards had a two-letter code within their local authority, and census output area an additional four digits within a ward.
The authority and ward codes were recognised by Eurostat as local administrative unit code levels 1 and 2 within the NUTS system.
Civil parishes
An overlapping system encoded civil parish areas. Parishes were represented by an additional three digits within their local authority:
List of codes for counties and districts
The codes for counties and districts were as follows.
Also showing NUTS(3) codes thus: (UKH12)
Greater London
These codes became active following local government changes in 1986.
00AA (UKI11) City of London
00AB (UKI21) Barking and Dagenham
00AC (UKI23) Barnet
00AD (UKI21) Bexley
00AE (UKI23) Brent
00AF (UKI22) Bromley
00AG (UKI11) Camden
00AH (UKI22) Croydon
00AJ (UKI23) Ealing
00AK (UKI21) Enfield
00AL (UKI21) Greenwich
00AM (UKI12) Hackney
00AN (UKI11) Hammersmith and Fulham
00AP (UKI12) Haringey
00AQ (UKI23) Harrow
00AR (UKI21) Havering
00AS (UKI23) Hillingdon
00AT (UKI23) Hounslow
00AU (UKI12) Islington
00AW (UKI11) Kensington and Chelsea
00AX (UKI22) Kingston upon Thames
00AY (UKI12) Lambeth
00AZ (UKI12) Lewisham
00BA (UKI22) Merton
00BB (UKI12) Newham
00BC (UKI21) Redbridge
00BD (UKI23) Richmond upon Thames
00BE (UKI12) Southwark
00BF (UKI22) Sutton
00BG (UKI12) Tower Hamlets
00BH (UKI21) Waltham Forest
00BJ (UKI11) Wandsworth
00BK (UKI11) Westminster
Metropolitan counties
These codes became active following local government changes in 1986.
“ONS coding system” enters the record as code used in the United Kingdom for tabulating statistical data. Crown Archives preserves that source wording while asking what coding, system and code can confirm, complicate or overturn.
Why this record matters
“ONS coding system” is worth following because a concise public description often conceals a longer documentary argument. Here, coding, system and code provides the most credible route into that argument.
The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated Aug 9, 2026. The linked authority identifier is Q123418904. None of the 0 selected statements returned an explicit reference. The first chronological checks are 2011 and 1986.
Overview language is designed for orientation and should not be treated as a substitute for the evidence cited beneath it. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
- Subject orientation
- Search vocabulary
- Locating named sources
The closest primary source, responsible institution and strongest cited specialist reference.
Three-step research path
- Establish the record: confirm the title “ONS coding system”, its source revision and the description used here.
- Expand the search: follow ONS coding system primary sources, ONS coding system archive and coding research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “ONS coding system”?
- What terminology or title could unlock a more precise catalogue search?
- Which institution is responsible for the underlying evidence?
Search terms from this dossier
This entry incorporates text from “ONS coding system” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.