I need some help from the Jewish members of the panel,?

If you can prove he has put a tracker and cctv equipment onto her car without her knowing, it is probably illegal (though I am not sure, since they are married and it is the UK,and I don't know anything about UK laws) and if it is illegal, he should probably reported to the police. It may or may not be your business to stick your nose in but that is your decision to worry about--if you do decide to take action, I would report him to the police if what he has done is actually criminal. Outing him in public is against Torah, and I am not sure how telling his rabbi would help much--if the man feels good enough to be having an affair, I have a feeling he probably won't listen to his rabbi anyways.