Hi MrsL,
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.
The parcel or courier company (for example, Royal Mail or Parcelforce) is responsible for taking goods through UK customs.
Please see below link for more information.
Tax and customs for goods sent from abroad
You can use this service to find a commodity code for goods you’re importing to or exporting from the UK and check if there’s duty or VAT to pay find out about suspensions or reductions.
Trade Tariff: look up commodity codes, duty and VAT rates
Thank you.