Amazon UK Purchases That Are Being Shipped From The EU - Will There Be Extra Charges In Future?

Every once in a while, I buy items from Amazon or Amazon Warehouse (UK) and it turns out they're actually being shipped from the EU. It's not made apparent at checkout - you only realise once the item has shipped.

So, after 31st December, does this mean that either these items won't be available to purchase for us in the UK, or I'll have a nice unexpected Customs charge in the near future? (I have a few orders processing from Germany and Italy).

I can't remember any order from Europe that's been sent by Royal Mail, it's nearly always Amazon.
Tried to see if there were previous Discussions, but couldn't find anything.

Thanks for any insights Happy New Year when it comes

Edit 11th January: I'm NOT referring to third-party seller purchases. My query is about items sold by Amazon themselves, specifically from the UK site.
I assumed EU-stocked Amazon UK items would no longer be listed, see here - then this happened‌