This case is local for me - the school is a couple of miles from where I live.
I recall when my wife was Head of a local primary school and she enquired about installing razor wire on the tops of fences to discourage vandals, and she was advised that any injuries caused to trespassers could involve the school in a civil legal action.
The same scenario applies here, although I do struggle with the concept of protecting intruders against injuries.
It does appear though that when tested on this occasion, such protection was found to be invalid, and the family will not win damages from the local council.
I sympathise entirely with this young man's lifelong cost for his adolescent stupidity, but I am pleased that a marker has been put down that holding businesses responsible for not protecting intruders is not something that the law is willing to entertain, which has to be a victory for common sense.