My air compressor has gone on the TCR after 6 years from new. I have enjoyed some saunal experiences this week with the aircon blowing hot air into the cabin so unlike in winter when you're not quite sure if it's working properly or not, I had that question answered.
VW parts have quoted £1,108.80 (part number 5Q0816803D). Even the parts guy sounded a bit sheepish giving me the figure and tried providing it without VAT to make it seem less like theft. I said something about Veyrons, cold days in hell and disappeared to do better on the Internet.
If anyone else is faced with the need to replace theirs, Deutsche Car Parts are selling Denso air compressors (which are OE) at the moment for £454.99. Ordinarily £700. I was going to replace with a Lucas but it's comparable to the OE Denso. Really great service from the guys at DCP who I've not used but would based on the experience I've had.
Shared in case it helps someone else out.