Guides

Reference material on UK addressing, postcodes, telephone numbering and safe test data.

• The UK Postcode Format Explained: Areas, Districts, Sectors and Units — A complete breakdown of how a UK postcode is built, the six permitted formats, the letters that can never appear, and the edge cases that break naive validation.
• Royal Mail Address Formatting: How to Lay Out a UK Address Correctly — The Royal Mail "Clear Addressing" conventions — line order, the post town in capitals, why the county is optional, and how to model UK addresses in a database.
• How UK Address Generators Work — and How to Tell a Good One — What separates a generator that produces usable UK test data from one that emits random noise: real districts, internal consistency, and honesty about what is fictional.
• Using Real Customer Data in Test Environments: The UK GDPR Problem — Copying production data into staging is processing personal data under UK GDPR. What the law actually requires, what the ICO has fined organisations for, and what to do instead.
• Why Your Address Form Rejects Perfectly Valid UK Addresses — Building names without numbers, BFPO, GIR 0AA, Northern Irish counties, Welsh street names and Scottish flat notation — the real addresses that break real forms.
• The UK Telephone Numbering Plan, and the Numbers Reserved for Fiction — How UK dialling codes are structured, why 020 7946 0xxx exists, and how to generate test phone numbers that cannot possibly ring a real person.
• Validating UK Postcodes in JavaScript, Python and SQL — Copy-paste implementations of correct UK postcode validation, normalisation and formatting, with the test cases that catch the usual mistakes.
• Where UK Address Data Comes From: PAF, ONSPD, OS Open Names and AddressBase — A practical guide to the authoritative UK address datasets, what each one contains, what it costs, and which one you actually need.