Thanks for quick repiles. I should have sorted this out sooner
I found the answer, they need a letter from Audi's homologation department showing it is Euro 4 emailed to the link Andrew posted. I have sent Audi the email already.
Some info on this forum:
https://forums.mercedesclub.org.uk/i...anding.169329/
What a bit of luck that late D2s are exempt!