A British postcode has two halves. The outward code — SW1A, RG5, B91 — is the district Royal Mail sorts to; the inward code narrows the post to a street or a handful of buildings. The August 2026 ONS Postcode Directory holds 3,016 districts in Great Britain's 120 postcode areas. District pages have been published under the address checker since 17 September 2026, and each of the 3,016 now has one. A page is built from nothing but what this server already holds: the national postcode directory, the places Ordnance Survey's Open Names publishes for each postcode, the roads the same file lists under each district, and the Companies House company snapshot. This guide says what is on such a page, where each number comes from, and what a district page will never tell you.
What a page carries
Every district page opens with the postcode area and its conventional name — SW is South West London, RG is Reading, B is Birmingham — from a hand-curated table of area names that is not read from any dataset. Then it carries what the weekly count measured for the district, and what is read when the page is rendered:
- The places. Open Names publishes, for every full postcode, the populated place, the district or borough, the county or unitary authority and the region it sits in. A district page lists the distinct places its postcodes carry, most frequent first, up to twenty-four. SW1A lists Greater London, London, the City of Westminster and Wandsworth; RG5 lists the South East, Woodley, Wokingham and Reading. The page's title names one of them: the place Open Names most often lists first for the district's postcodes, which is the populated place where Open Names names one and the borough where it does not — the City of Westminster for SW1A, Woodley for RG5, Solihull for B91. It is never called a post town. These are the names the checker matches a written town against, lenient to the borough and the region, so a page is also a preview of which towns an address in that district may honestly carry.
- Live and terminated postcodes. The directory keeps every code ever issued with its status, and the page counts both. SW1A has 145 live postcodes of 355; RG5 has 504 of 675. A terminated code is a real address that has moved on, not a typo, and the count of them says something about how much the district has been redeveloped.
- Sectors. A sector is the postcode less its last two characters: SW1A 2 of SW1A 2AA. The page tabulates each sector's live and terminated codes; SW1A's 145 live postcodes sit in SW1A 0 (3), SW1A 1 (67) and SW1A 2 (75).
- The roads. Open Names files every road under one district. The page counts the roads filed under this one and lists all of them, named roads first and numbered roads (A40, B4632, M4) after, folding everything past the first sixty into a disclosure: 33 for SW1A, beginning with Arlington Street, Bennet Street and Blue Ball Yard; 57 for WC2H; 285 for RG5, ending with the A3290. In the listing installed on 22 September 2026, 2,411 of the 2,752 districts with a road filed under them carry more than sixty, and BL1 carries the most, 1,540. The list is read from the listing when the page is rendered and cached for a day under the listing's version.
- A centroid. The mean position of the district's live postcodes, from the directory's coordinates. SW1A's is 51.50455, −0.13223, which is Whitehall. It locates the district, never a building.
- The nearest districts. The twelve districts whose centroids lie closest, by great-circle distance, among the indexable districts — those with a live postcode and a listed road — whichever postcode area they are in. WC2H's nearest are WC2E at 0.3 km and W1D at 0.4 km, and nine of SW1A's twelve are W1 and WC2 districts rather than SW ones. Every district has a page, but a district that is not indexable is never listed as anybody's neighbour. A district without a centroid, such as one with no live postcode, links the first twelve indexable districts of its own area instead.
- Companies. How many companies the Companies House snapshot lists with a registered office in the district and, where there are at least a hundred, how many of them are at addresses that 25 or more companies share; 25 is the count at which the address lookup reports a company cluster. WC2H has 91,283, of which 89,741 are at such addresses, in the 1 September 2026 snapshot as read on 23 September 2026; SW1A has 1,307, of which 674. These are counts only: the page never names an address or a company.
- The datasets. Which copy of the directory, which copy of Open Names and which Companies House snapshot the page was read from, with their versions and Open Government Licence v3.0 attributions, and a "Data synced on" line giving the newest of those versions. The versions are those of the copies installed on the server that rendered the page, so they move as each dataset is re-synced.
- A hand-off. A link into the address checker with the district prefilled, so a visitor who has found their district can check an address inside it, and the same road list as a call to the streets endpoint.
On 22 September 2026, counting the August 2026 directory, the warm command measured 3,042 districts: 3,016 in Great Britain, of which 2,752 are indexable, and 26 in the Channel Islands and the Isle of Man.
What makes a page indexable
A district page exists for every outward code the directory holds a postcode for, but only a page with at least one live postcode and at least one listed road is offered to search engines and listed in the sitemap; the others render with a noindex directive. On 22 September 2026 that left 264 British districts unindexed: 144 whose codes are all terminated, and 120 with live codes but no road filed under them. The rule is the same one the country pages follow: a page earns its place with data of its own, and a district of terminated codes and no roads has nothing to say that the index page does not.
Districts are keyed exactly, by the code with its last three characters removed, never by prefix: SW1 does not swallow SW10, and B9 does not swallow B91. The index page lists every district grouped by area and says how many of them carry both, so the 2,752 are browsable rather than one long list.
What a district page will never tell you
Three things, each stated on the page itself.
A directory says whether a code is in use, never who is there. Nothing on a district page, and nothing in the address product, names a resident, a household or an occupant, and no field ever will; the counts are of codes, places, roads and companies.
A road is filed under one district. Open Names files each named road under a single outward code, while a long road runs through several, so a street missing from a district's list may be filed under its neighbour's. That is why the checker never scores a British street it cannot find — on 16 September 2026, 87.3 percent of 49,106 street lines taken from Companies House registered offices matched by district, a share of those street lines and not of every filing — and why the road count on a page is a count of what is filed there, not of every road a resident would say is in the district.
There is no open register of buildings in Britain. Every full British address list derives from the Royal Mail Postcode Address File, which is licensed, so a district page can list roads and places but never say whether number 12 stands on one of them; exists stays null for a British address until a licensed partner is configured. Can you look up UK addresses from a postcode for free? says the rest.
Why Northern Ireland is missing
The directory excludes BT postcodes by design: their reuse needs a licence from Land and Property Services that the open directory does not carry, so no Northern Irish district has a page, and none is counted in the 3,016. That is a licensing fact, not a coverage claim, and the directory's attribution, printed on every district page, says so.
The Channel Islands and the Isle of Man
The directory does carry the Channel Islands and the Isle of Man: the GY, JE and IM areas, 26 districts between them. They are Crown Dependencies, not part of Great Britain, so the index lists them apart from the British areas and leaves them out of its counts. OS Open Names does not cover them, so their pages count postcodes and sectors but list no roads, are not indexed and carry no Companies House count. The copy of the August 2026 directory installed on 22 September 2026 carries no coordinate for any of their 13,173 postcodes either, so their pages have no centroid and name no nearest districts.
Using the pages
For a person, the pages are the quickest answer to "which towns does RG5 cover" and "is SW1A 2AA still a live code", and the hand-off turns the answer into a check. For a developer, they are the human-readable face of what the streets endpoint answers for a British postcode — the same listing, the same versions — and a reminder that the API's British answers are about streets and codes, with the building deliberately left to the licensed list. For a search engine they are what the product knows about a district, dated, attributed and refreshed every Saturday after the places sync.