1) Find the customs form you need
Items sent via Royal Mail:
For items worth up to £270, make sure you include a completed and signed CN22 customs label. Here's how to complete a CN22 form.
For items worth over £270, complete and sign a CN23 form. You can ask staff for help with this in-branch.
Items sent with Parcelforce:
Irrespective of value, items will require a customs declaration form which you can pick up in-branch. Any items sent with Parcelforce globalexpress will require the customs declaration form CP72 regardless of the destination
2) Complete, sign and attach custom forms
The sender is legally responsible for the information on the customs declaration, so it’s important to ensure that it is accurate and complete.
Put your customs form on the front of the item, as near as possible to the top left-hand corner - just don't cover up the address.