Under Royal Mail restrictions, orders containing more than 4 bottles of liquid or any bottle over 150ml cannot be sent by post (they will be siezed and destroyed without compensation), so have to be sent by Courier. Unfortunately, we are still waiting for our web software providers to write a module to enable us to block shipping methods on a product-by-product basis, so it is still possible to accidentally select a method which can't be used. This item is to cover the cost of upgrading to the appropriate courier delivery service from the one you selected. We are very sorry about this - it is down to Royal Mail regulations and beyond our control.