This question was answered on 29th November 2017
In the 2015 study, Fatal opioid poisoning: a counterfactual model to estimate the preventive effect of treatment for opioid use disorder in England, a research group including Public Health England estimated that the English treatment system prevented an average of 880 deaths each year from opioid-related poisoning between April 2008 and March 2011. A copy of the study is attached.