“The longer the government went on creating policies that conflicted with the scientific evidence, the more harm those policies would do, not least because they undermined our ability to give a consistent public-health message, especially around the dangers of alcohol. The more hysterical and exaggerated any Home Secretary was about the harms of cannabis, the less credibility they would have in the eyes of the teenagers binge-drinking themselves into comas every day. If we’re going to minimise harm, we have to have a way of measuring it, and a policy framework that can respond to this evidence. Yet even comparing the dangers of cannabis and alcohol was considered a “political” act that overstepped my remit as a scientist and physician.”