Thanks Alan for drawing attention to this problem. It's not something I've really encountered but it's good to know what to look out for and what action to take (photo, grid ref, report).
Challengers and other walkers can make an important contribution in ensuring that only legal traps are used. It's impossible for the police/animal welfare groups etc to monitor every area, so it's good that we can help. Hopefully, we can help deter those who seek to flout the law.