Yes you can find belly dancing costume shops in the UK. One source is eBay. EBay has many UK stores online and many belly dancing outfit selections. You will find skirts, harem pants, headbands and veils plus coin belts, just for starters. On eBay prices start as low as 99 Euro. Most items are under 35 Euro. Euros are valued at slightly more than 1, about 1.32. Another store in the UK is named Egyptian Dreams. Accessories, shoes and other footwear, arm bands and coin items are available online at a reasonable price. Maybe you would like a custom made outfit. Stores such as DonAngeli will create your outfit. They are located at P.O. Box 567 Redhill Surrey, England, RH1 3WS
