Below is some, perhaps, useful info regarding shipping to and receiving from the UK from now on. This primarily applies to GIFTS. Shipping something as GOODS is more complicated. But yes, a customs declaration needs to added when sending FROM the UK to another country and also TO the UK for GIFTS as well.
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Regarding receiving something from EU/abroad if you are based in the UK.
"When receiving goods from abroad, recipients may have to pay VAT and duties. The VAT and duties will be applied depending on the type and value of the goods. For gifts over £39 and goods over £135, Royal Mail may collect the VAT and customs duties on behalf of HM Revenue & Customs (HMRC). from the recipient prior to delivery. Letters, postcards and documents are usually exempt."
https://www.royalmail.com/brexitSo, mark it with less than £39 when sending to the UK.
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I suppose every EU country has slightly different rules when it comes to non-EU imports so here are just 3 different examples.
UK to Ireland:
"Customs charges will not apply if the item is a gift with a value of under €45."
https://www.irishtimes.com/news/ireland/irish-news/brexit-to-hit-parcel-post-to-and-from-britain-1.4447643Non-EU (which UK now is) to Denmark:
"If as a private individual you receive a gift from another private individual in a country outside the EU, you must pay VAT and customs duty if the gift has a value of more than DKK 360."
https://skat.dk/skat.aspx?oid=2244328UK to Sweden:
"This means that when you receive or shop online from the UK, you must pay VAT and any customs duties before the goods can be delivered."
https://www.postnord.se/en/sending/preparations/customs-information/customs-information-regarding-brexitBasically, shipping a few items to Ireland and Denmark should be fine - albeit with some minor delays for customs processing - while it seems to mean that someone based in Sweden may want to avoid buying from the UK unless they want to pay extra fees.
Considering that these are only 3 EU countries out of 27 I think it may be worthwhile to check your national postal service/customs service. I'd imagine that Sweden is in the minority regarding this.