I personally have never had any bad experiences with the police and think most of them are just doing their best in a difficult job, would say we have a lot more trustworthy police force than most other countries as well even in the developed world
I can see why a lot of people don't though and there's been quite a few things recently which will have decreased trust in the force as a whole; all the stuff that's come out about Hillsborough, what happened in the Stephen Lawrence case, the Jean Charles de Menezes shooting, the Mark Duggan shooting, and most recently the Andrew Mitchell plebgate stuff. It seems they have been guilty of fabricating or meddling with key evidence on quite a few occasions, I read quite a good article on it about a month back:
http://www.telegraph.co.uk/news/ukne...r-anarchy.html