There are figures available August 2016 for Police stop and searches in Camden. Click here for them. The vast majority of stops are for drugs on people aged between 15 and 24 and disproportionately targeted are Black males. You could argue that they produce few arrests e.g of 440 searches in August only 93 were arrested (21.1%). How many were found guilty of an offence is a not stated.
The Drug Legal Advice organisation , Release, have produced their own guides on Stop and Search. A PDF can be downloaded here.