Indeed!
For goods sent from overseas and sold directly to UK consumers without OMP involvement, the overseas seller will be required to register and account for the VAT to HMRC.
In other words, non-online marketplace sellers (eg Thomann, or Jerzy Droyd, or that little boutique guitar seller you used to use in Aachen) have to register for UK VAT and charge that VAT on any sales to UK buyers, In other words, if a shop wants to trade with Britain it needs to go through all the rigmarole of submitting a VAT return to HMRC every 3 months... That's why our garden centre no longer trades with 3 of our Lovely Little Things suppliers in Europe - they didn't want the extra grief!