Thanks for the comments guys. I think the shock/.anger is wearing off a little. Only a little.
The police officer that came out today also recommended security film but also cautioned that he had seen many VW/Seat/Skoda vehicles suffer the same fate and said he'd had a few where they came back if not successful after attempt one or once the insurance had paid for a shiny new replacement.
The original RCD310 is going back in next week when I have time to sort the mess.
I've yet to decide what to do re the insurance. So far it will cost me £70 window excess and £42 for the two parts (window trim and stereo trim) as I can't yet see any damage to the wiring loom etc. I think the scratches to the paintwork don't justify a respray so will just have to live with those

The dashboard marks where they have used a screwdriver should be covered up with the trim piece.
The cost of the RNS510 from a dealer is £2447 inc VAT!!

Insurance company have asked if I want to submit a claim but as yet not sure as they limit audio to £1000 on what they will pay for. I don't want them to pay towards an RNS510 that I won't fit and them only pay me out if I produce an invoice for it! Plus I need to think of the potential impact to my no-claims bonus etc. even though it is protected.
Hoping to ring my broker tomorrow to discuss / get advice.