The place you sent the box then repacks it and mails it to the UK. Somehow the UK thinks that you and only you have broken the law.
Buyer beware: this calculation is based on several derivations of napkin maths with very fixed assumptions. It should be accurate to the nearest zettabyte.
You send a packet to your ISP with an address on top. That packet physically travels to your nearest exchange and then the network figures out how to route it to the recipient's real location.
In addition, the recipient's IP address tells you nothing about who or where they are. It's fundamentally un-knowable from the sender's perspective, no matter what the UK wants you to think. IP addresses are not evidence of physical location.
When you receive a packet, there is no way to know where in the world it came from or where it wants to go. It's just a number. You can make guesses but it's still just reading tea leaves.
To believe that IP geolocation is in any way reliable is a gross misunderstanding of TCP/IP and networks in general.