Where I am (NSW, Australia), the current "best legal advice" about recording your interactions with police is that it's legal to record conversations (even secretly), but it's not legal to play those recordings to anyone else. So you can't bring up your recording of a conversation with a police officer as evidence in court. What you _can_ do though, is if an officer lies about the contents or existence of a conversation, you can tell the court you've got a recording that proves a police officer has told the court something that's not true - and the court can then (legally) ask to hear your recording.
(Disclaimer: I am not a lawyer - nor do I play one on youtube. If this matters to you, seek competent legal advice before acting on this information…)