How do I expand my US Shopify store into the UK: VAT, fulfillment, entity, and inventory?

A UK storefront is not the hard part. Who owns the stock, who files VAT, and where a return can land are. Those are three operating questions. They are not one Shopify Markets toggle. This is operating mechanics, not tax advice and not legal advice. Talk to a UK advisor before you treat stock-in-country as harmless. Do not invent a registration threshold or a VAT rate and run the company off it.

DDP from the US or a UK 3PL

Ship DDP from the US while one carrier stack and one US returns address still work. Stand up a UK 3PL when you need UK carriers, UK packing inserts, a marketplace that will not replenish from the US, or a returns address customers will actually use. Storing goods in the UK generally triggers VAT registration even if you keep the inventory on the US books. A UK legal entity is a separate decision from a UK 3PL, and both are separate from the VAT registration. Do not confuse the tax trigger with the systems trigger with the company trigger. The entity-vs-3PL fork is its own post. Here the job is to keep the four workstreams from collapsing into "we turned on the UK market."

HS codes and DDP setup

Country is a first-class field on the product and on every inbound. One HS code for the UK, one for the US. The US ten-digit HTS is not the UK code. Get VAT, EORI, and a storefront DDP disclaimer in place before you collect duty at checkout. DDP is three jobs: checkout collects, customs declares a value that matches what the customer paid, the carrier knows who pays. Those three do not travel together. Incoterm often fails to sync even when HS and origin do.

UK WAC and who owns the stock

Duty capitalizes on the allocation date, so UK WAC is not US WAC. Price off landed cost in GBP, not supplier FOB in USD. If a UK entity will own the stock, set that entity's base currency to GBP before the first receipt. Updating FX later does not revalue stock you already hold. If US Co still owns the units at a UK 3PL, they are US inventory sitting in the UK. US WAC, US COGS when the US storefront ships. Renaming a Shopify location does not move ownership.

UK returns and per-country channels

Returns need a receiving node in the UK, not a pretty portal. A Shopify refund with no receipt is invisible inventory. Outbound customs lines are built at pack. Return commercial invoices are built when the label is generated. Portal labels skip that, so DHL and UPS often will not quote. Test UK return labels the same way you test outbound. UK and EU are not one node after Brexit. Same 3PL, different division codes, different packing slips, different returns addresses. Amazon UK inbound is not Amazon US inbound. Per-country channels are not equivalent even on the same platform.