I tried the dealer (Listers Nuneaton) twice:
1st time i got; duuuuh, that's not on our system.
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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.
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If it helps, the part number is......
1K0 853 675 AN