Wow - that's nuts!
Admittedly, in the video it's hard to tell just how much "clearance" they have in a turn. But that driver (in a training scenario apparently) is taking a WIDE turn, and so we lose perspective as to how close the cab/overhang might get in this handheld video.
I'm also concerned about the weight distribution ... Right at 47 sec into the video, you can see the approximate location of the hitch relative to the truck bed. It appears that the base of the hitch is (essentially) right over the rear axle. That's not typically where you'd want it to be; ahead of the axle is optimum for loading the front axle a bit. If that hitch were any further back, it would be unloading the front axle (not good whatsoever). And as mentioned by others, the turning radius is seriously compromised by such a short bed. There are things called "sliding hitches" which essentially rotate on a cam as the vehicle enters a tight turn; it moves the hitch orientation further back as the turn gets tighter. These are made for "short bed" trucks (typically full size trucks with 6.5' beds rather than full-size 8' bed). But I don't think you'd get a lot of "reach" from one of these in a small Ranger bed.
It's the UK, so I do understand that (especially in rural areas) they just have smaller roads, lower speeds, etc. And so maybe the risks of such a set up (small truck; large 5vr) are not as prominent. But I sure would want a larger truck for something like that.