Every full list of British addresses derives from Royal Mail's Postcode Address File, and reselling it needs a licence, which is why a British address has never been able to answer exists from open data and still cannot. What Britain does publish openly is its streets. Ordnance Survey's Open Names, released under the Open Government Licence, lists every named and numbered road in Great Britain with the postcode district it runs through, and since 16 September 2026 Spaw installs it as a register of streets.
What it confirms
A British address whose street Open Names lists under the address's postcode district answers match_level: street and confirmation.street: register. That is a real check: the street exists, in the part of the country the postcode names. A street Open Names does not list there answers match_level: none and confirmation.street: unconfirmed, and — this is the part to read carefully — carries no weight.
exists stays null either way. A register of streets has nothing to say about a building, and the answer will not pretend otherwise. The building question in Great Britain has exactly one honest source, the licensed file, and until a partner is enabled it is unanswered.
How a street is keyed
Open Names files each road under one postcode district — the outward half of a postcode, the SW1A of SW1A 2AA — so a written address is keyed the same way: the street name folded to its comparison form, under the district of the postcode it was written with. Bilingual roads are indexed under both names, so Castle Street and Heol y Castell in Cardiff both match.
The district is also the register's limit. A long road runs through several districts, and Open Names files it under one of them: Baker Street sits under W1U, so 221B Baker Street written with its real postcode NW1 6XE does not match. Measured on 16 September 2026, district keying matched 87.3 percent of 49,106 street lines taken from Companies House registered offices. Filing every road under every district of its settlement or borough recovered three more points at thirteen times the index size, and was not worth it.
That is a share of street lines, not of filings. The recall table on the address product page measures something wider: every Sunday it draws whole filings, whatever their lines hold and whether or not their postcode stands, and sends each through the ordinary lookup. In a run of 23 September 2026, 1,441 of 2,000 filings drawn from the 1 September 2026 snapshot, 72 percent, matched a street. Neither number is the share of British addresses Open Names knows; both are what the matcher makes of addresses other people wrote.
The 87.3 percent is why the register is declared partial and why street_not_found never fires for a British address. Under complete coverage a miss would be a denial and would cost 20 points; at 87 percent it would be a false denial one time in eight, on the biggest market the product has. So a miss is reported as exactly what it is — a street the register did not confirm — and scored as nothing.
The town, at last
The same release names, for every postcode, the populated place, the district or borough, the county or unitary authority and the region it lies in. Until now a British answer could not say whether the town matched the postcode, because the postcode directory publishes no post town; on 16 September 2026, 1,742,466 of 1,749,109 installed postcodes gained those places.
The check is lenient on purpose, because British towns are written several ways. "London" and "Westminster" both confirm SW1A 2AA, the first as the region and the second as the borough. "Reading" for a Woodley postcode is not one of that postcode's places but is a place the directory lists elsewhere in the RG area, so it reads confirmation.locality: postcode_area with locality_matches_postcode: false and no weight: a post town written for a settlement is how envelopes are addressed. "Manchester" for a London postcode is found nowhere in the area, and that one carries the locality_mismatch weight of 30.
What is installed, and how often
Open Names is republished quarterly, and the register syncs monthly with a freshness window of 45 days, so a copy older than that is flagged on the status page. The release is about a hundred megabytes; on 16 September 2026 the 999,065 road rows compiled to 876,830 street keys in a 7.3-megabyte index in about thirty seconds from the local file, and applying the places to the postcode directory took another thirty-five. Street names are folded before they are keyed, so "Rd" and "Road", "St" and "Street" and the two spellings of a Welsh road all land on one key, and a written address is folded the same way before it is looked up.
The file covers Great Britain — England, Scotland and Wales. Northern Ireland's postcodes are excluded from the directory in the first place, because reusing them needs a Land & Property Services licence, and Open Names carries no Northern Irish roads, so a BT address answers postcode_status: null — the directory was not consulted — rather than as a code that does not exist, and it never gets a street match from Open Names, which carries no weight either way.
Reading a British answer
Put together, a British answer on a server with the postcode directory and Open Names installed can now say: the postcode is live or terminated, the town belongs to it, the street exists in that district, and — from Companies House — how many companies are registered at the building. What it cannot say is whether the building stands, and the fields that would say so, exists and the licensed is_deliverable, answer null rather than guess.