Normally you charge VAT on your sales, and reclaim VAT on your purchases. However, if you sell second-hand goods, works of art, antiques or collectibles, there may have been no VAT for you to reclaim when you bought them. You may be able to use a VAT margin scheme. This enables you to account for VAT only on the difference between the price you paid for an item and the price at which you sell it - your margin. You won't pay any VAT if you don't make a profit on a deal. You can still use standard VAT accounting for other sales and purchases such as overheads
Normally you charge VAT on your sales, and reclaim VAT on your purchases. However, if you sell second-hand goods, works of art, antiques or collectibles, there may have been no VAT for you to reclaim when you bought them. You may be able to use a VAT margin scheme. This enables you to account for VAT only on the difference between the price you paid for an item and the price at which you sell it - your margin. You won't pay any VAT if you don't make a profit on a deal. You can still use standard VAT accounting for other sales and purchases such as overheads
More here.
http://www.hmrc.gov.uk/vat/start/schemes/margin.htm