First I've heard of the increase, but since I ordered my car back in October, I have a contract signed by both myself and the dealer I bought it from with all the prices listed (including the basic list price, options and VAT). Any attempt to alter this would clearly be a breach of contract, so I'm not expecting any problems.
I would expect that the price you pay should be the price quoted at the time you ordered the car (and therefore presumably paid a deposit, as I did) rather than at the time of delivery. This should then give a fixed price for the car regardless of any delays caused by either Audi themselves or the dealer - if either party tries to change this then they are in breach of contract.
I'm no expert on the law, but this seems pretty cut-and-dried to me!