Stop feeding the troll. His knowledge of the legal system surrounding the rather old principle of the duty of care owed to trespassers is laughable (confirmed by the House of Lords in 1972.) It's also probably largely based upon reading papers like the Mail or the Express. Well known for their quality legal reporting...
Let's take his example of the poor Night guard. someone breaks in to and dies. Can the company be sued? Maybe, it entirely depends on what killed them. If they jumped off a crane taking a selfie, no chance.
The duty under the 1984 Act is to "take such care as is reasonable in all the circumstances of the case to see that the non-visitor does not suffer injury on the premises by reason of the danger concerned". There are other pre-requisites such as knowledge of the danger which exists.
But what about the signs? Well, the Act says: "Any duty owed by virtue of this section in respect of a risk may, in an appropriate case, be discharged by taking such steps as are reasonable in all the circumstances of the case to give warning of the danger concerned or to discourage persons from incurring the risk."
So, if you put up signs, there is a good chance you will be ok, as you have warned people. If the risk is sufficiently clear then "No duty is owed by virtue of this section to any person in respect of risks willingly accepted as his by that person"
The children issue with warnings is different, because not all children can read. and the 1957 act also provides that we should "be prepared for children to be less careful than adults". This is just common sense, especially when we see that kids like Teflon loved nothing better than to play on building sites. What if, on that building site there was a large hole covered by a tarp, or a big gap in a fence surrounding an electric transformer? If you leave a danger like that, then you are stupid enough to deserve to pay for it.
Oon the whole, as long as the person takes reasonable, common sense precautions to avoid dangers or protect people from them they will be ok.
So that's what the law says, essentially apply common sense, if there is a gap in a railway fence, and the railway company knows there is a gap in the railway fence, if a child wanders through the gap, and is hurt or killed, of course that is negligent. If an adult did the same thing, there may not be negligence provided there was sufficient warning signs. the adult took the risk voluntarily. (I would argue that you wouldn't even need the signs, it's pretty common knowledge not to cross railway lines, but people do it every day.)
My point is, the legal system of this country is nowhere near as risk-averse as industry. The prospect of being sued is actually more scary to organisations than the reality.