Hi,
Anything posted or couriered to you from another country goes through customs to check it is not banned or restricted and you pay the right tax and ‘duty’ on it.
This includes anything new or used that you:
• buy online
• buy abroad and send back to the UK
• receive as a gift
There are certain thresholds before which the custom charges applied, more information on below link:
Tax and customs for goods sent from abroad: Overview
Thank you