Originally Posted by Tezcatlipoca

The Channel Islands are not part of the UK - they belong to the Crown (they're a Crown Possession, or Crown Dependency, or something like that).

They have their own government, & their own laws & tax rules.

They currently enjoy tax haven status, although apparently the EU is not happy with that.

As others have said -

Anything imported from the Channel Islands is liable for VAT & import duty, if over the £18 personal import limit. If you don't get charged, it's just good luck. Customs don't inspect every package.