People capitalise nouns to show something has high status, for example, ‘Chief Executive’ or ‘Minister’. I’ve seen cases where member-funded organisations refer to their members as Members to show they are important. Some companies do the same thing to their Valued Customers.
This is a mistake! Don’t do this!
The more formal or important a document, the more likely people are to capitalise ‘just in case’ — we wouldn’t want to offend anybody by demoting them with a little letter. So we end up with documents where every third word is capitalised. The effect: visual clutter. (Visual clutter makes text harder to read and harder to understand, so avoid it like the plague.)
‘Status has nothing to do with capitals.’ Say it again. ‘Status has nothing to do with capitals.’
Capitalise nouns that refer to a specific thing, not a generic thing. So write the Ministry of Education the first time you mention it. If you mention it again, you might write the Ministry (a short version of the name; it’s still specific, so it’s still capitalised. You just haven’t bothered to write the name in full.)
In the same document, you might write that three ministries came up with a change in policy. You’d use lowercase because you’re using the term generically now. You’re not referring to a specific ministry any more.
So, Police or police?
If you’re writing about the New Zealand Police, you’ll use capitals. Same if you write Police for short. Police Officer Molly Malone will be capitalised because she’s a specific person.
But if two police officers attended the scene of a crime, they’ll be lower case — we don’t care who they are specifically, just that they attended. Even one police officer could attend a crime and they’d still be lowercase, as the term isn’t standing for the short version of someone’s name. Reporters could write that police believe the driver left the scene, as they’re using the term generically. (They don’t mean the New Zealand Police, as a whole entity, believes the driver left the scene.)
If in doubt? Lowercase.