Re: What about the VAT?
When Apple Ireland sells to Apple UK, or to any other customer that has a VAT registration number in a country other than Ireland, Apple Ireland doesn't charge VAT on the sale.
Apple UK has to pay UK VAT on the products it imports from Apple Ireland based on wholesale price, which will be the same as the price Apple Ireland sells to other retailers such as Dixons Carphone. It can then simultaneously claim that VAT back, so the net effect is no payment due, and no refund receivable.
When Apple UK sells to retail customers in the UK, or to UK based businesses, it has to charge VAT on the sale, and pay that over to HMRC. If it sells to retail customers in other EU countries, it has to charge the VAT rate applicable in that country and pay it over to the local tax authorities there.