A lot of smaller merchants and online shops find it too complicated to comply with the new requirement to register with HMRC for VAT purposes. Increasing number of them simply refuse to ship any items to the UK. Charging VAT at the point of import before this year worked just fine.
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BBC and some other papers (https://www.bbc.co.uk/news/business-55530721) already wrote articles about Dutch bike store and several other overseas retailers refusing to deal with British customers. Sometimes there are no alternatives for these smaller specialist retailers inside the UK. An attempt to make every possible company in the world register with HMRC is strange and unachievable, leading only to UK customers being locked out of services they were relying on.