You don't have to pay tax on goods purchased in the US - keep your receipts and you can get them refunded while still in the country. If you're visiting a city, ask the store where you can do this. However, you are liable to pay UK tax on any goods you bring in. I think you get an allowance but it's not very much (couple of �100). Wayne Rooney's girlfriend was caught bringing in extra goods just last week. I think you would have to pay the duty and probably a fine on top for not declaring.