1) If the word police is plural, then we have such a sentence
Police are here
Okay, no questions, but what to do with the tag question?
Police are here, aren't it?
or
Police are here, aren't they?
Because I think it wouldn't be
Police are here, aren't police?
We should change it for some pronoun
2) We can have some dialogue:
A: Do police work well?
B: Yes, it works very well
OR
A: Do police work well?
B: Yes, it work very well
OR
A: Do police work well?
B: Yes, they work very well
Actually it's the same point number 1, but anyway
Best Answer
The police are a group of people, and that overrides the idea of them being an entity, so you have to use a pronoun that can be applied to people - you want they.