WooCommerce Shipping Class

Using the WooCommerce 2.0.10 plugin I have a problem with assigning a shipping class to a product. My default option is free shipping, but I want to add an additional postage charge for specific products. So I added a flat rate shipping class, and assigned it to the product. But when I test the checkout the £4.99 shipping cost is not added to the cost of the product at checkout. Instead 2 radio buttons appear which allow the buyer to choose free shipping or the extra cost of £4.99. How do I get the £4.99 to be added automatically at checkout?