Politicians who want to celebrate the health of the British economy are always on the lookout for data to bolster their case, yet routinely neglect one consistent metric of success: immigration. People do not abandon the place of their birth and cross continents without expectation of a better life. It is a vote of confidence in the destination country.But it is politically difficult to celebrate this magnetism. A perception that new arrivals are on a mission to milk the benefits system and abuse the hospitality of the indigenous population is widespread yet false. Most come to work. Yet assertion of that fact doesn’t neutralise demand that the numbers come down. While the aggregate effect of immigration on GDP might be positive, the gain is meaningless in places where there is no palpable feeling of prosperity and demographic change feels sudden and uncontrolled. Those conditions did not wholly account for Britain’s vote to leave the EU but their contribution was significant enough that Theresa May has chosen to make an end to free movement of labour a non-negotiable clause of any Brexit deal. Even once ardent supporters of EU membership, such as former business secretary Vince Cable, say the economics of free movement are open to ambivalent interpretation.The PM’s decision solves a short-term problem (how to signal responsiveness to demands of many leave voters) but it brings her no closer to answering the deeper question – how to combine a border regime that is fluid enough to preserve economic dynamism and rigorous enough to inspire public confidence? . The scale of that challenge gets clearer daily. Yesterday, Andrea Leadsom, the environment secretary, suggested that farmers should be able to hire EU workers post-Brexit. Yet such seasonal influxes of labourers, bringing high densities of transient workers, are precisely the kind of migration that provokes resentment among longer-established populations. It is unlikely she would have suggested such a compromise last year, when drumming up leave votes.It is not just farmers who want to continue importing workers. The NHS and social care services rely on foreign-born staff. The City of London wants to hire in the global marketplace. So do universities, retailers and internationally integrated industries.One way to deal with these dilemmas is a move to more sector-specific and regional arrangements. Industries could sponsor incomers, whose immigration status would be pegged to their local job. Something along those lines is proposed in a report published today by MPs and peers. The all-party parliamentary group on social integration suggests visa devolution in imitation of Canada, where autonomous provinces help to set their own immigration requirements. This has the appeal of matching migration decisions to local conditions but is fraught with practical difficulty – the task of enforcing geographically circumscribed visas without offence to civil liberties, for example. Canada’s arrangements are predicated on its relaxedness about overall increases in the number of people in a vast country with low population density. Those conditions do not pertain in Britain.No immigration regime for Britain can satisfy both political pressure for lower numbers and employer demands for flexibility. And there is no prospect of a return to the culturally homogenous workplaces and town centres of yore. Pretending otherwise, raising false hopes that the past can be restored, is a proven recipe for disappointment and anger. A wiser route would be to shift the emphasis on to conditions that give workers a greater sense of security in a labour market that offers ever fewer prospects of a job for life. That means proper enforcement of the minimum wage; punishment of gangmasters who exploit illegal migration; incentives for employers who develop the skills of their staff; and investment in retraining so that the vagaries of the market do not turn periods of unemployment into lifelong redundancy. That is a long-term project to make British workers more resilient and attractive to employers.Fear of competition from foreigners will never be entirely neutralised, nor should nostalgia for the days before labour was globally mobile be dismissed as luddite or xenophobic. Those are understandable responses in a climate of insecurity. The prime minister is currently indulging the belief that Brexit will provide the necessary relief. It won’t. The demand for a better border-control regime is politically impossible to ignore, but the time is long overdue for Mrs May to show more honesty about the scale and complexity of the task.