State control and supply. Drugs provided by the state will have a guarantee of good quality, with checks so the NHS can monitor how and where they are used, and will be taxed to high heaven so the state can get revenue from the druggies (but the prices will still be lower than they are now). Combine with a two-handed policy of buying up raw material in Afghanistan in return for a certain amount of influence there. Whatever the Taliban can do, they can't outbid us in the market.