my 2 cents on the points raised by you and ismene: the police do so pathetically at anything but catching minor drug offenders that it does seem like they view this as an acheivement. they get most of their info from tip offs so don't really even work anything out themselves. its lazy and easy and keeps arrest rates high.
You're spot on chinup. Jancrow seems to think hassling "Petty small time drug users" is something the police don't want to do. On the contrary the police view this as a great and valuable acheivement which they'll always quote when trying to impress the public.
I read one Chief constable saying he didn't mind breaking down drug users doors "even if we don't find any drugs because it lets the drug user know we are the boss". That means he's perfectly happy for the taxpayer to foot the bill for the door simply because he wants to let small-time drug users know who the boss is.