Ian,
Thanks for the reply- I've heard back from Streetwise and it is the linkage which goes to the valve which has failed. Part 4DO 616241A. And about an hour labour. So not a big job. Audi apparently want £60 for this part- You wouldn't happen to have any lying around would you? Will give you a ring in the morning anyway.
Unfortunately I didn't get any pictures yesterday as I was in a bit of a tiz getting it home, then parked it on a hill so the effect would be lost! I can assure you though that it was a proper handful to drive! Regretting lack of pics though
Mitch has now re-set the suspension at the correct level. I assume it's worthwhile keeping the self-levelling function? He did offer to put a bolt in the valve which would hold it at the current level, but without the automatic levelling.