ahhh, now that's the good part and the reason i went for the XK one!
The position shown in those pictures is where the lever sits when it's on AND off!!
Basically...
You pull it up to engage, then when you let go the lever drops back to that position.
To disengage it, you pull the lever up, then press the button and lower it and it goes off!
It's one of the features that they always demonstrate to new XK owners as it always catches people out, and even then I've driven away a few times with it engaged as i didn't notice the warning light on the dash as the dash hadn't finished cycling through the setup checks before i started moving <doh>