The rain has let up a bit, and I've managed to get a couple of photos. Only with my phone so they're not fantastic, and the car behind was parked a bit close to get a clear view. They show the Towbar stowed (you can just see the head hanging down below bumper level - arrowed). Deployed, half deployed, a shot of the button location and a better shot of of the button.
Also there is an exploded diagram of the system is at:
The option was about £600 from the factory. I can can see why it would be so expensive to retrofit, but that is still a vast amount of money. Having said that, it is the mutts nuts as towbars go.