Broadly speaking, the VED rate applies to the list price plus options of the vehicle at the time of purchase, so it depends on the terms of your order. If you have paperwork that shows a deposit has been paid and an agreed price that will not change then the list price at the time will apply, but if you have just put your name on a waiting list then the price may be affected by price changes. It would be wise to make this clear with the dealership when you place your order to ensure you are not subject to price changes.