Yes, give DTD a call - they don't charge you to talk to them. If you have a part ex that you want rid of then that can complicate things going the broker route (more so if the car you want to trade isn't a VW or VAG car).
Sometimes the dealer can meet you halfway and give you a far better p/x.
Count on the DTD price and assume WBAC.com valuation on your part ex, then see if the cost to change is higher with the local dealer and try to get them to meet you at same cost to change (they will probably be offering you significantly more p/x than the WBAC.com valuation if it is a car that they wouldn't mind selling on their used forecourts).
Example.
1. DTD offer you £3500 off your new car and WBAC.com offer you £12k for your part ex.
2. Local dealer offer you £1500 off your new car and £14k for your part ex.
Same cost to change for both scenarios. If there is no p/x in the equation, don't mess about with the dealer any more, get onto DTD.