@Jo**
it's not random in the sense that every single thing has a HS code and a duty associated with it.
It's something Europeans living in the EU aren't usually aware of because we usually buy stuff from elsewhere in the EU where there is no duty and no extra tax and don't have to go through all this.
You are going to have the exact same thing in the UK once you have properly Brexited, you will need to look up the exact HS code for anything coming in to the UK to find out how much duty is due. And this varies depending on the item. Just like in Thailand.
Look at this example from UK customs, five different duty rates for different types of silk! It's the same everywhere, you are just more sheltered from it if you are in a large single market and buy everything from within that market (EU, US, etc.)
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