If you are visiting the U.K. from the U.S.A., you can claim back the VAT spent on purchases here in the U.K. You must request a VAT Refund form from the shop where they make your purchases, and then put them in an envelope and leave it unsealed. There is not a Customs desk at the terminal, so you will need to post the envelope in the Customs box, which is usually found just after the X-Ray machines. Customs collect these regularly and will process the refunds accordingly.