Shortly after switching the engine off the dashboard wakes up again. Pulling the park brake switch also switches the engine off. It seemed like an interaction between the buttons on the panel. I removed, stripped and cleaned the switch panel (the one with the gear selector built in) as it was filthy but with no improvement. There was no tendency for it to happen with the panel unplugged so I bought a replacement panel, unfortunately it still does it! Is this similar to anything anyone else has experienced? Can anyone give me an idea of the architecture of this system?
I've had it a while, I think I need to find the diagnostic scans!

I haven't seen that fault but it might be worth looking at the module on the right of boot for corroded connections. Also the module on the right of the accelerator pedal.
Regards Ian.

Sorry for the late update, I blame Covid!
I found a multi plug to the left of the transmission tunnel (basically between the front passenger seat and the tunnel). It was absolutely vile with spilt Coke. Gave it a good clean and all working. Wrapped a plastic bag over it to try and prevent a re-occurrence. Customer did admit that he doesn't treat his cars very well!