Well it's back.
The TMC is fixed and the summertime option is back and enabled with the GPS clock switched back on. The clock is currently correct, although only time will tell whether it stays that way and the summertime option doesn't vanish again. The DAB programme times are still wrong however, showing the GMT times and not adding an hour for BST!
They said they'd "calibrated" it again, plus sorted out the coding and installed a software update. Don't know how much of that to believe really as all the software version numbers are unchanged. Have told them to keep on at Audi about the DAB times though. It's not really a big issue but just a minor annoyance that they can't get something that simple right. Main thing is TMC is working again and I have my car back after suffering with an 8P Sportback for three days (I hate 5-door cars!!).