UK has a statutory police union -- that is, the government set up its own union for them: https://en.wikipedia.org/wiki/Police_Federation_of_England_a...

Interesting quote from there:

"Police officers hold office and are not employees. Each officer is an independent legal official and not an "agent of the police force, police authority or government". This allows the police their unique status and notionally provides the citizens of the UK a protection from any government that might wish unlawfully to use the police as an instrument against them."