Once you've completed your order, a full VAT invoice is available from the following places:
Order confirmation/shipping confirmation email - a text URL to your invoice in PDF format can be found on your order confirmation email (sent after you complete the checkout process/when your order has shipped).
Customer account page - when logged in to your account (https://thepihut.com/account), your invoice can be downloaded in PDF format from the "Orders" section of your account (example below).