I think you would be better off asking a solicitor first.
It is bad enough that the media gave bull bars bad publicity to a point that bull bars are banned or had to be redesigned to pass safety.
If you accidently hit a child, and the child dies. The parent could claim your home-made bull bar is not up to safety standards. Your defence barrister could argue that even a shop bought bull bar would kill a child anyway, but then the prosecutor could argue that a shop bought bull bar had been known to either seriously hurt or killed children (meaning a 50:50 chance), while your DIY bull bar killed a child on the first go (100% chance of a kill).
Could it be possible to wrap the scaffolding tubes with some kind of pipe insulation to minimize the dangers to people? (It won't stop getting someone killed, but hopefully minimize the chances?)
As for what effects it have on the Land Rover, I have no idea, I guess other members knows better.