Hi AJB2494
Looking at your video, its looks very similar to my motor a few months ago. Same symptoms, same sound, same smoke....
More about it here:
https://www.landyzone.co.uk/land-rover/terrible-sound-from-the-engine.283038/
and here.
https://www.landyzone.co.uk/posts/3527653/
My motor had jumped one tooth on the lower chain. This happened when I turned the starting key, saw the glowplug symbol coming on and released the starter key at the same moment. The starter had probably not turned the crankshaft around enough to overcome the first compression stroke, and the build up compression in the cylinder reversed the direction of rotation of the crankshaft enough to make the chain jump one tooth. Also the brief turn of the crankshaft did not build enough oil pressure to firm up the chain tensioner.
You can not see this one tooth jump unless you have the camshaft blocking tool and the locking pin in the flywheel. By just looking at the cam-lobes it is not obvious.
Major work to get everything sorted out.
You must pull the head and the sump to gain access to the chains and tensioners.
Better change all wear parts when you are down there.
(chain tensioner, chains, chain-guides, gaskets, camshaft sprocket bolt, headgasket, headbolts, consider doing the serpentine belts, water pump and thermostat too)
Also a few special tools are worth to buy, as the high pressure pipe key, 17mm I think, strong torx cup's as the head bolts are torx as is the camshaft bolt.
Could also be worth the money to have the head vacuum tested before re installation. Just to check if any of the valves has had an unpleasant encounter with a piston.
Good luck
Larsern