Fair enough Waldo as a collective of the three, but when did the Police stop using the word Force? Genuine Q by the way - I've never, as far as I am aware, heard the phrase Police Service.
Like Haggisdj, I have been hearing this term for about 10 years. It's not a PC thing, so much as a rebranding excercise done by the police themselves to promote a cuddlier and more consumer friendly image.
Service is actually a better description of what they're supposed to be doing, so I don't object to the change at all.