The potency issue is a perennial red herring thrown up by those opposed to reform since the mid 1970s. While the potency of herbal cannabis may have increased, this is because high quality material is more readily available (i.e. grown in the UK from 'pedigree' seeds as sinsemilla), rather than seeded compressed material grown abroad and semi-decomposed before it reaches the consumer. High-quality herbal and resin has been seized by customs since the 1970s (See Gough TA Ed 1991 The Analysis of Drugs of Abuse). The potency of resin, if anything, would appear to have declined in recent years. The FSS quotes resin potencies between 3 and 7%, the range I have encountered is from 0.5% ('Formula') to 12% (Nepalese/Minali), with 'soap bar' typically around 4-6%. Resin typically contains significant quantities of CBD as well as THC, whereas herbal contains little if any CBD. One argument is that more potent material may have harm-reduction potential, in that less herbal material needs to be smoked to achieve the same high. Unfortunately where this argument breaks down is with the UK/European practice of mixing herbal cannabis with tobacco, where putting less 'weed' in the 'spliff' would only increase the tobacco-bearing proportion.