When shopping in the UK you will be charged Value Added Tax (VAT) on all your purchases. Similar to Sales Tax in other countries, VAT is not chargeable on Children’s clothes, books or food (plus a few other smaller categories such as Airline fuel!), but is included on everyday non essential items.
Unlike many States in the US, VAT is included in the ticket prices of items and not added in at the point of sale, so what you see is what you pay at the counter. Receipts should show this tax.
If you are a visitor from outside the EU, you are entitled to reclaim this tax on your departure from the country. To do this you must shop in stores that carry this logo, as they have the necessary forms that you need to have. Some stores have a minimum spend of around £30-£50 to fill out a form for you, as any less is only a couple of pounds after administration charges.
You then take your goods, receipts and form to the airport with you, or by post and they will refund your taxes, minus a small admin charge. You will however be liable for any local taxes on arrival in your home country, but doing this stops you being charged twice.