I do wonder, though, just how 'in charge' of the driving this unauthorised person really was,
A 10yr old could do it. The first time you "drive" you are following instruction and nothing else. I still remember the first time I "drove" I sat in the seat, put my feet on the Drivers Safety Device, my hand on the controller, and looked out the front window. That's pretty much all I did.
I've been up the front of a Javelin at 140mph and you can literally drive with the blinds down.
and were lives really at risk? I wouldn't presume to know the answers, but hopefully others do.
No more than any other day. Probably a slight increase in risk due to the additional people in the cab but that will depend on the cab discipline shown by everyone.