Was in Boots the other day & the security guard was at the till blethering to the lady on the cash desk & he was talking about a police friend of his. Apparently the police have been told to arrest respectable-looking people who cause public breach of the peace but not people who look a bit dodgy/druggie etc. The thinking behind this is respectable folks will turn up for their court appearance whereas junkies or whatever won't & will then cause the hassle of warrants, postponed trials etc which costs a lot of taxpayers' money.
So if some drugged up/pissed numpty is harrassing you in the street you'll just have to grin & bear it & console yourself that at least your tax money won't be wasted taking him or her to court.