A second hand book shop is required to add a 20% value added tax (VAT) to its products by law. However, charity shops are not required to do so. Similarly, second hand book shops purchase used books for resale, whereas charity shops are given used books for free. If a second hand book shop purchases a book for £5 and resells it for £15 (VAT included in the price).

How much more profit is generated by selling the same book at a charity shop for the same price?