I wonder if the Mail is bending the facts here for the sake of a clickbait headline.
The choir is called "The Derbyshire Constabulary Male Voice Choir". The Mail story states that "From June onwards the choir, which is made up of civilians, will change its name to the Derbyshire Community Male Voice Choir." Well, frankly, if the members of the choir are not members of the Derbyshire Constabulary, why should the choir be named to imply that they are? And apparently they wear police uniform tunics when they perform in public, which I am surprised was allowed.
I suspect that when the choir was created it was all police officers, but over time there weren't enough singers so they recruited from outside, and now none of the choristers are policemen. And it's time to update the name to reflect that.