How an address is written in the United Kingdom

An address in the United Kingdom is written in this order: house number and street name, then post town, then postcode, with the post town and the postcode in capitals. The strongest checks here are the postcode and the street: the ONS Postcode Directory (August 2026), with 2,665,797 postcodes in England, Scotland, Wales, the Channel Islands and the Isle of Man, 1,760,216 of them live and Northern Ireland's BT codes excluded; Ordnance Survey's OS Open Names lists 888,215 streets in Great Britain (version 1 November 2026), but no buildings.

The order the lines go in

The parts are named rather than filled in: Spaw does not know an address in the United Kingdom and will not invent one. This block is produced by the same function that rewrites a real address, so the line order, the capitals the United Kingdom asks for and any text its operator prints on every envelope are the checker's own behaviour rather than a second description of it.

Organisation
12 Street name
Flat or unit
POST TOWN
POSTCODE

No recipient line: nothing in the response is about a person, so the name the envelope carries is not part of what is checked.

field	called here	required	capitals
organization	Organisation	optional	—
addressLine1	Street name	required	—
addressLine2	Flat or unit	optional	—
locality	Post town	required	yes
postalCode	Postcode	required	yes

No house-number rule is carried for the United Kingdom, so the international default is used: the house number comes before the street name. The postcode is written after the town.

Can Spaw tell whether an address in the United Kingdom exists?

Partly: the street, never the building. Ordnance Survey's OS Open Names lists 888,215 streets in Great Britain (version 1 November 2026), and no buildings. A street register can confirm that a street is where an address puts it but never that a building is, so exists answers null for every address in the United Kingdom: not evaluated, never no. Its streets are filed by postcode district, so a street is confirmed inside the district the postcode names.

A postcode directory answers a different question. The postcode is settled separately by the ONS Postcode Directory, which is recorded as complete for England, Scotland, Wales, the Channel Islands and the Isle of Man: one it does not hold answers postcode_not_found, and a retired one reads as retired rather than as a typo. Northern Ireland's BT codes are left out of it and never looked up, so an address carrying one answers postcode_status null rather than postcode_not_found.

register	covers	lists	coverage	version
Ordnance Survey's OS Open Names os-open-names	Great Britain	888,215 streets	partial	2026-11-01

Further reading: How to read an address-existence answer, What a street match means in Great Britain and Can you look up UK addresses from a postcode for free?.

Check an address in the United Kingdom

The same lookup the API runs, with United Kingdom already selected.

Live demo

POST /demo/address · no key needed

try:

Response

Look up any address to see the full API response, straight from the live service. The country decides which format it is read against.

Every field in the response Get your API key

The postcode

Postcodes in the United Kingdom are checked against the pattern below rather than a description of it, because the shape is too particular to summarise without losing a case.

pattern GIR ?0AA|(?:(?:AB|AL|B|BA|BB|BD|BF|BH|BL|BN|BR|BS|BT|BX|CA|CB|CF|CH|CM|CO|CR|CT|CV|CW|DA|DD|DE|DG|DH|DL|DN|DT|DY|E|EC|EH|EN|EX|FK|FY|G|GL|GY|GU|HA|HD|HG|HP|HR|HS|HU|HX|IG|IM|IP|IV|JE|KA|KT|KW|KY|L|LA|LD|LE|LL|LN|LS|LU|M|ME|MK|ML|N|NE|NG|NN|NP|NR|NW|OL|OX|PA|PE|PH|PL|PO|PR|RG|RH|RM|S|SA|SE|SG|SK|SL|SM|SN|SO|SP|SR|SS|ST|SW|SY|TA|TD|TF|TN|TQ|TR|TS|TW|UB|W|WA|WC|WD|WF|WN|WR|WS|WV|YO|ZE)(?:\d[\dA-Z]? ?\d[ABD-HJLN-UW-Z]{2}))|BFPO ?\d{1,4}

A national directory is installed for the United Kingdom, so a postcode here is not only checked for shape but looked up: 2,665,797 postcodes in England, Scotland, Wales, the Channel Islands and the Isle of Man from the ONS Postcode Directory, version 2026-08, of which 1,760,216 are live and 905,581 have been retired. A retired code is usually a real address with an out-of-date code rather than a typo, so it is scored rather than refused.Great Britain’s postcodes in numbers breaks those counts down by postcode area and by month.

Northern Ireland's BT codes are excluded from that directory: reusing them needs a separate licence, so an address carrying one is answered as though no directory were installed — postcode_status null, the directory not consulted — rather than as though the code did not exist.

The half of a postcode before the space is its postcode district (each has a page), and the letters it opens with are its postcode area: a town that is not one of the postcode's own places is checked against the places of that area before it is called a mismatch.

What the United Kingdom calls an address that is not a front door

A PO box, a private mailbox and the other kinds of delivery point below are told apart by the words written on the address, never by a list of whose box is whose. The rows marked as the operator's own words are taken from the addressing guide of the postal operator in the United Kingdom; the others are international spellings, not the operator's own. All of them are what the checker reads, and because an entry is carried for the United Kingdom, an address here with none of them answers street.

address_type	written as
private_mailbox Private mailbox at a mail-receiving agency	PMBinternational spellings the checker also reads
po_box Post-office box	PO BOX, P O BOXinternational spellings the checker also reads
general_delivery Held at the counter for collection	POSTE RESTANTEinternational spellings the checker also reads
military Military and diplomatic mail	BFPOthe operator's own words

What can be checked for an address in the United Kingdom

Read from the datasets this server holds right now, not written into the page. For most countries the answer is the written form and the postcode shape and nothing beyond them — in particular not the row people assume is always there.

check	for GB	what the answer means
Written form	yes	The address is split into the country's own parts and rewritten in the order above. A missing required part is named in one typed reason rather than a general failure.
postcode pattern	yes	Checked against the pattern the table carries for the United Kingdom. A value that does not match answers invalid_postal_code.
postcode exists	yes	2,665,797 postcodes in England, Scotland, Wales, the Channel Islands and the Isle of Man from the ONS Postcode Directory, live and terminated ones apart, so a retired code reads as retired rather than as a typo.
Kind of delivery point	yes	The operator's own box words are carried for the United Kingdom, so an address with no marker answers street rather than unknown.
Street exists	yes	888,215 streets in Great Britain from Ordnance Survey's OS Open Names, keyed by postcode district. match_level answers street on a hit.
Building exists	no	Ordnance Survey's OS Open Names lists streets, not buildings, so exists answers null here: not evaluated, never no. A street can be confirmed; a building cannot.
Companies at the address	yes	An open company register is installed for this country, so the number of companies giving the address as their registered office is counted, and a published threshold marks it as a mail drop.
Known mailbox branch	yes	Mailbox operators' own published branch lists cover this country, and the answer names the operator that matched.
Post actually arrives	no	Not from this page, and not from open data in any country: whether post is delivered, and the vacant, residential and agency flags that go with it, are the postal service's own licensed product. Those fields answer deliverability_checked: false rather than a guess.

Null means not evaluated, never no.

Other countries

Sources

Google's Address Data Service · address-formats 2026-09-05© Google LLC, CC BY 4.0 (Google Address Data Service); initial import via commerceguys/addressing (MIT)
The postal operators' addressing guides · address-rules 2026-09-17
The ONS Postcode Directory · ons-postcode-directory 2026-08Contains ONS, OS and Royal Mail data © Crown copyright and database right 2026, Open Government Licence v3.0. Northern Ireland postcodes are excluded: their reuse needs a Land & Property Services licence.
The open company registers · company-registers 2026-10-01Companies House free company data product, Open Government Licence v3.0
Mailbox operators' published branch lists · mail-drop-locations 2026-10-31

Data synced on 2026-11-01: the newest version among the datasets listed above.

Wrong result, or is it about you? If this tool said something you think is wrong, tell us and a person reads it. If Spaw is holding data about you and you never signed up here — a customer may have had your address verified, or reported that a message to it bounced — erase it yourself, confirmed by mail to that address and with no account needed.

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