This is gospel.
Any orders placed (by this I mean the car has to be ordered by the dealer on our system) by the 31st August will be price protected irrespective of when the vehicle is delivered.
They will not however be price protected against VAT as this is out of the control of the retailer/Volkswagen.
The price increase is 3.2% on Golf but this will only affect anyone ordering on the 1st September onwards.
Paying in full by the 31st August is nonsense. It won't be for target purposes though as the sale doesn't count until it's registered (assuming you are waiting for a 59 plate). It's more likely to do with cash flow. Some dealers have a policy that you need to pay in full three or four days before delivery, that may be the case for those of you taking your cars in the first week of Sept.
In my experience, these confusions tend to happen when the sales manager hasn't fully explained to the sales people and they assume/exagerate/cover their ar$es with customers.

Hope this helps