I tried the dealer (Listers Nuneaton) twice:
1st time i got; duuuuh, that's not on our system.
2nd time the guy emailed VW Germany as it is covered on an application note for special editions. He was going to call me when he got a response. I never heard from him again.
I emailed VW UK with the query. They said "Contact your local dealer"
In the end I bought a second hand one from markymark on here.
If it helps, the part number is......
1K0 853 675 AN