Read the result’s coverage label
The GeoNames UK file used in this release contains the first part of postcodes. PostalMap labels these results as prefixes. A result such as SW1A is a broader search area, not a complete postcode to paste onto a mailing label.
Use the complete address
A town name can produce many candidate areas. Use the building and street details with Royal Mail’s postcode finder to confirm the delivery address. Preserve the letters, digits and spacing in the returned code.
Avoid filling a form by guessing
If a checkout asks for a complete postcode, a prefix may be rejected or match too many addresses. Ask the recipient or use the official finder. PostalMap’s country directory and map help you explore areas but do not replace that final check.