Audi have announced that new fuel filler necks will be fitted on future A4, A5 and Q5 models (including the 'S' models of each variant) as a first step and those in Europe that order the above mentioned models at the time this article was written would get the new filler system on their new cars. The new fuel filler necks will have a system or flap that will only open for the larger sized diesel nozzle and will keep its flap shut for the smaller petrol type fuel nozzle.
It also seems that this is a no cost upgrade for the Audi cars mentioned above. So future customers will not get charged for this 'upgrade'. This is obviously a very good thing to consumers who already have to deal with rising fuel prices and other cost of living issues. And to those that ask whether you can pour diesel into a petrol Audi, you most probably cannot, as the fuel filler neck in a petrol car is small and the diesel nozzle would not fit.
One more thing that hasn't been announced is the fact on the next Audi models which will have this upgrade or whether all this would filter down to all other Volkswagen-Audi Group diesel vehicles.