One of the things about dealing with most of the folk the Police are likely to encounter is that it engenders an incredible degree of cynicism. I've never done the job myself, but I've worked with similar clienteles, and it can be extremely difficult to maintain a balanced view of life when 8 out of ten people lie outrageously to you, even when there's no point in doing so, and especially when you catch them in the lie.
I think the current policing culture engenders a certain amount of cynicsm in the leadership (both in terms of government, and higher management) which is overly target driven, stupidly bureaucratic, and removes a huge amount of the discretion that officers used to be able to exercise in the course of their duties. Whilst I wouldn't go as far as my esteemed colleague Mr. Pig, I do think that the way policing is run currently here in the UK is a recipe for disaster, and needs a serious rethink.
Books like "David Copperfield"'s "Wasting Police Time", Ellie Bloggs' "Diary of an On Call Girl" give an idea of what it's like to be a serving officer currently. "Inspector Gadget"'s "Perverting the Course of Justice" gives the view from a higher level.