Key data ingredients for UK postcode lookup

The data behind your user interface is vital to user experience

When adding UK postcode lookup or address validation to an online form, it’s easy to concentrate on how the UI elements will look and forget about the data that powers the search.

The data powering address searches can make the difference between your users finding their address in one quick search, or not being able to find their address at all and having to enter their entire address manually.

Some potential customers will even take to social media to complain that they could not find their address.


If you're reviewing and comparing different postcode lookup APIs, there are some other datasets that you should be aware of:

Daily data updates

1. Royal Mail PAF (refreshed daily)

In the UK the best source of address data is the Postcode Address File (PAF) from Royal Mail; a massive data file containing 29.5 million residential and commercial addresses in the UK.

PAF is far from static with changes being made daily, based on property and business owners informing Royal Mail directly or the postmen and women delivering the mail making note of changes.

Altogether these changes total around 4,000 per day, including new houses being added, demolished buildings being removed and organisation names being updated when businesses move premises.

Royal Mail also provide a monthly version of PAF but clearly an API that relies on monthly updates will not provide the latest and most up-to-date addresses.

Multiple Residence data

2. Multiple Residence

Multiple Residence is a dataset from Royal Mail of around 700,000 addresses mainly comprised of flats that exist behind a shared letterbox. In PAF these would show up as one delivery point, however there might 50 addresses behind that delivery point.

That’s a lot of addresses to overlook - without them you might be missing a vital part of the address to ensure a package is delivered to the correct apartment, or your customers will have to manually edit their address to add this in, risking mistakes being made.

3. BFPO addresses

The British Forces Post Office (BFPO) is a separate postal service for the men and women serving in HM Forces around the world, with addresses which don’t include geographic information, to allow mail to be sent to someone regardless of where they are currently stationed.

Since 2012 Royal Mail have worked with BFPO to include postcodes alongside a BFPO number and address to allow inclusion in online ordering services that require a postcode to be entered.

Not Yet Built data

4. Not Yet Built

Not Yet Built from Royal Mail contains addresses that are at the planning-approved or under-construction phase but that are not yet being delivered to by Royal Mail.

Insurance firms, utility providers and estate agents can make use of them to validate that a building is going to exist in the future, in order to arrange installation of broadband for example.

The Not Yet Built dataset can be searched independently with PostCoder Web, if you need to be able to only look for addresses still under construction.

All four in PostCoder Web

Our web API provides easy search access to all four of these datasets.

Find out more about PostCoder Web »



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