I mean, the law _is_ selectively enforced, and it's the CPS' job to decide who to prosecute. That's not so much a legal issue as a social/structure and purpose of police issue.

Moreover in terms of the general law and how that law should or shouldn't be written, I can only recommend this discussion which is more detailed than any discussion we could have here and a more informed source:

http://barristerblogger.com/2018/03/24/its-time-to-change-th...