Brexit has changed the legal aspects of deliveries to the United Kingdom. After the UK left European Union custom/tax zone, the VAT tax payments are more complicated. When selling to UK consumers like modellers, we have to charge UK Vat for order amounts below 135 GBP. We pay Tax to the HM Revenue and Customs then. Orders of the net value exceeding 135 GBP are subject to export with 0% VAT, but the consumer has to pay this Tax when receiving the shipment.
The Shop system will block orders of value below 135 GBP when the delivery place is in the UK. For smooth transaction, please set GBP currency, clicking a globe icon, like on picture below: