You are saying that reports on the BBC, and in enquiries by the IPCC, and Met admissions of shoddy work, and having to issue apologies, and all the rest of it, are not to be trusted?
In recent weeks I have read about one policeman being found guilty of sex offences, a finding of inappropriate care of a man in the cells who ended up dead, and another officer being (jailed? sacked? something) for not bothering to follow up / take evidence on women who went to the a Sapphire unit.
I am sure even you can think of some major ones over the years - Jean Charles Menezes, Ian Tomlinson, Jon Warboys, Kirk Reid.
Also the stuff that came out with the phone hacking investigations / Leveson enquiry.
A quick google gave me this from a few days ago met fuck up again although it isn't one I had seen before. So that's another strike against them on my mental list, which I didn't even know about before.
Hope that helps to answer your question.