[Tannaton]

^^^ That

You can buy a kit with the trailer module and full wiring harness including 13-pin socket that simply plugs in to the cars existing loom through existing sockets - that costs around £120 - £150.

Then you need the software installing at the dealer, which should cost about the same or less, the labour probably twice the cost of the software.

If you can find a good indie with a licensed VIDA instance - that would be cheaper.