It's a lot of tricky work needing a lot of the roof frame dismantled with care and replaced with the same care, otherwise you will forever have a sunroof seal leak if not done correctly.
If you have glass insurance cover, get a quote from a V.W main dealer who has access to an EOS trained roof technician - talk to V.W UK customer services. Not every shop has these technicians and if you have to drive a hundred miles with an overnight stay, consider it? Expect the repair quote to be very high on labor. Don't go near a windscreen replacement firm, they probably wouldn't do it anyway. If you have to pay the first £50-100 you still have a bargain!
The replacement glass is relatively cheap compared to labor costs and getting the job done correctly. I've done a rear window glass and that's kids play compared to the sunroof.