At least twice as many school pupils smoke cannabis as smoke tobacco. Cannabis is illegal, tobacco is legal. If legality meant anything, the figures should be the other way round. Smoking, like alcohol and narcotic drugs, is both enjoyable and harmful. The state’s job is to regulate the balance. Health education, together with nudge measures like banning smoking in public places, have cut tobacco consumption steadily since 2000. The number of smokers has fallen in the past decade from 20% to 13% of the population. The one alarming development has been the use of vaping by children, with more than 20% of 11 to 17-year-olds now saying they’ve tried it, which is why the government’s proposed restriction on flavoured vapes is long overdue and is rightly directed at manufacturers blatantly promoting them to teenagers. How effective it would be remains to be seen. Rishi Sunak’s plan to ban tobacco sales altogether for all entering adulthood, however, is bizarre. Cigarettes will become a sort of halfway house between vaping and cannabis. They will establish a widening gulf between two classes of adults: those who were aged 18 or younger today and an annually dwindling band of legal purchasers who can prove their antiquity, presumably by passport, to a tobacconist. Tory libertarians, led by Liz Truss, may use cliches about nanny states – usually dependent on who gets to be nanny – but the proposal rings hollow. Imposing arbitrary age limits on shoppers for what will remain the legal activity of smoking is classic Home Office control freakery. Evasion will be easy. Acquisition will be merely an inconvenience. Black markets will flourish and the chief victims will be shopkeepers and tax gatherers. This, in part, is why a similar proposal in New Zealand has recently collapsed. The fallacy of restricting the consumption of a product by trying to limit supply is a standard economics issue. It does not curb demand, it merely increases price. Half a century of Britain’s supply-obsessed “war on drugs” is proof enough of that, as were America’s attempts at prohibiting alcohol. Tobacco use in Britain is declining – despite it levelling off during Covid – largely through public health and education. Let it continue to decline. Meanwhile, as central government powers up what will be a costly and bureaucratic tobacco-banning directorate, it is curbing the one initiative that has clearly proved effective. The Health Foundation reports that austerity has cut the resources going to local council “stop-smoking” services by 45%. This is centralist public policy at its most counterproductive. As for priorities, the policy is even crazier. The cost to the NHS of smoking-related illness – calculated at some £3bn annually – is half the cost of obesity. Yet the government lies spineless in the face of the food lobby over a condition that now afflicts more than a quarter of the British population. This surely merits the status of a crisis. Yet what is the chance of Rishi Sunak banning the sale of pizzas and doughnuts to under-18s? Simon Jenkins is a Guardian columnist