Hello Dave. I called the local dealers to find out what their mechanics knew. They said their aftermarket dash cams are fixed with sticky pads so maybe your b-i-l's is an aftermarket one. I didn't have the vin to hand when I checked realoem yesterday morning so I wasn't sure I was looking at the right model, but I've found the vin now though so I can be sure of looking at the right model. Perhaps I can fathom out this double lining, if it really is a thing. Also there are speakers in the roof, as per my previous post. Theoretically - and as already paid for - Halfords should be able to do this; and they do factor in 2 1/2 hours for doing it which I would have thought was enough time even when taking the extra tailgate work into consideration. Halfords is Road Angel's preferred installer (!). We don't have the panoramic roof, although the previous one did - and a not very good sunroof!
I think first I'll call the other two local Halfords and see what they have to say, as between the tailgate videos and your information I think I understand it all and there's clearly not much to do, barring accessing the loom at the hinge, that they wouldn't be doing on any car. My husband's not very technical and work takes up a lot of our time otherwise I think we could do it ourselves.
Thanks so much Dave for being so helpful - you'll be please to know that I'll keep you posted!!
Sue