I run bush cables full time passed 2 mots with them on and never been questions, as for the danger of injuring someone by the time they have managed to get above the height of the landy, got past the solid steel winch bumper over the light guards and then hit the bush cables they will be doing well.
So where do you stop ???winch bumpers that are pedestrian friendly but don't use them as they will not take the weight..... rock sliders they could also be a problem too.
How about the ladder on the back leading up to the roof rack there could be a danger there too..... mind you may be the roof rack could cause an injury.........
Be proud of the landy you drive ......
Thats because there is no part of the MOT that would look at them or a ruling to make them unsafe - therefore cant be failed on them.
BUT
If you had to stand up in court and defend their fitment because someone had been thrown up and halfed by one, you may well get accused of fitting accessories (and subsequently dangerous) to your vehicle when you didn't have need for them at the time of incident. There is an argument that they can be easily fitted and removed for road use.
This is why steel bull bars are no longer allowed to be fitted by manufacturers (and also a lot of insurance companies wont permit them), and also why Jaguar no longer have their mascot on the bonnet (and why the Rolls Royce Spirit of Ecstasy is retractable).
On the scale of potential injury to a person the wires are pretty severe compared to a winch bumper as a percentage (its unlikely that you bumper will remove limbs).
So, not technically illegal by the book, but there is nothing to stop you being judged irresponsible for what you do to your car. Its a choice you have to make for yourself.