In the absence of any responses to my previous post I have had to take the car to the local Audi garage.
They confirm that the problem is "No Spark".
This is the good news. The bad news is that everything they have tested so far appears fine other than one of the Reference sensors. I have also suggested that they check the current input "15" at the back of the fuse box which has given problems before.
Any other bright ideas or experience to share?