Sadly the reason you suggest is all too prevalent, but no, the council need not worry. If something is built, it needs to be built properly. If it's built properly and you use it and injure yourself through your own incompetence, then the landowner has nothing to worry about. If it's badly built, then it's a different story, of course, but even then the claimant would need to prove that the landowner knew about the dangerous state and allowed it. Those jumps weren't badly built.