I recently bought a RR Classic Defender hybrid with the 3.9 V8 motor. Whole vehicle shortened to 100 inches. It goes like a bat out of hell on a straight line, but tends to spit you out extremely dangerously on a rough sealed road at reasonable speeds.

The whole steering mechanism has been re-done. I suspect the rear shocks are perhaps too light?

Photos attached reveal the wheel articulation.

What would cause this dangerous problem - it scares the pants off of you.

mmmm from my limited knowledge of motorsport preparation i would say what you got there is definatley a spring damper shock combination problem trouble is to keep the cars off road ability ur gonna lose an amount of on road handling as is the case with even the mildest off roaders, what you need to do is find the right balance between the two, i'm sure there must be a mathematical formula for this i just dont know it, personally i'd be looking at stiffer shocks or maybe adjustables trouble is its a very hit and miss approach and can become very expensive especially when you dont get it right, alternatively get on the phone to an off road race prep company check out the mags for ideas and remember get it right and you will have some serious kick ass equipment get it wrong and its gonna hurt, good luck

Have you got the range rovers anti roll bars or are they removed?

Yeah, I would say that the sway bars have been removed.
Also have the front toe checked.