I look back at this thread with relief - some of the advice would have been bad in the long run (let alone costing more at the time)!
http://forum.a8parts.co.uk/showthread.php?t=4917
The car ran well for the next 50k miles until I sold it, but then I think the new owner remove and mapped out the DPF on a quest for fuel economy and simplicity.
Change tends to be slow, so I suspect by the time this comes in it may not be economical to "repair" many of these cars - which is possibly an intended side effect!?