A postcode district is the outward code of a British postcode, everything before the space — SW1A, RG5, B91 — the area Royal Mail sorts to before the inward code narrows the post to a street or a building, and the unit Ordnance Survey's Open Names files each road under. The August 2026 ONS Postcode Directory installed here holds 3,016 of them in Great Britain's 120 postcode areas.
What Spaw answers
Two things read the district. The register of streets for Great Britain is keyed by it, so a British street match means the road is filed under the district of the postcode you wrote; a road that runs through several districts is filed under one, which is why a miss there never scores. And every district has a page of its own, listed on the British postcode districts index: the places Open Names lists for its postcodes, the live and terminated postcode counts from the national directory, sector by sector, every road filed under it (named roads first, and past sixty the rest folded away), a centroid, the twelve nearest districts that are indexable, how many companies Companies House lists with a registered office there, and a hand-off into the address checker with the district prefilled. Only a district with at least one live postcode and one listed road is indexable: with that directory and the Open Names listing of 22 September 2026 installed here, 2,752 of the 3,016 are. The Channel Islands and the Isle of Man, which the directory also carries, have pages too, but they are not part of Great Britain and not counted among them.
What it does not mean
A district is not an address, and neither is a full postcode: the guide Can you look up UK addresses from a postcode for free? says why a code that identifies a street or a few buildings still says nothing about a particular one. Northern Irish districts are absent because BT postcodes are not in the directory — their reuse needs a Land & Property Services licence — and a district page says whether codes are in use, never who is there.