The Best, the Brightest and the British Politicians obsess over what the country does for immigrants. They might instead ask what immigrants could do for the countryâ€”if they were allowed. link In 1972, your correspondent's grandfather came to Britain with his wife and two children. Fleeing Idi Amin's Uganda, he left a large house and a successful family firm for a small subsidized flat in west London. He earned fresh qualifications and eventually found work as a broker and then an underwriter. With the wealth of opportunities that Britain offered, the family repaid the initial handouts several times over. This trajectory was once unremarkable among immigrants to Britain, but has now become nearly impossible. If my family came to Britain today they would most likely face deportation after failing to meet stringent residence requirements. If seeking asylum, they would be forced into indefinite welfare reliance. Britain began tightening immigration requirements in the late 1960s, when politicians discovered they could win votes by blaming foreigners for everything from rising violence to public debt. Trouble is, the shifting mishmash of quotas, rules and thresholds have done little to check either crime or welfare rolls. They do hamper incoming foreignersâ€”at least, those who want to work and follow the law. Consider Hussain Zulfiquar Alvi. The Pakistani citizen completed his studies in Britain in 2005, at which point a clinic in Kensington deemed him valuable enough to hire as a physiotherapy assistant. When Mr. Alvi applied for a visa extension in 2009, he was informed that the government had changed its criteria for "skilled" work in 2008 and that he no longer qualified. He would have to return to Pakistan. The Kensington clinic, presumably, would have to find a new physiotherapy assistant. Mr. Alvi appealed and last month the U.K. Supreme Court ruled that the Home Office had acted unlawfully in trying to deport him. The government had implemented the 2008 changes under the executive power of "royal prerogative"â€”without a debate in Parliament. The Home Office has regularly tinkered with immigration rules using these powers, but July's court ruling requires that any changes that can lead to deportation must first go through Parliament. The Home Office has now dutifully offered Parliament its latest "statement of changes." The update runs 288 pages long, not including the accompanying memorandum. Meanwhile, a House of Lords committee has called for "clarification" about the status of all immigration-rule changes since 2008, when Parliament last debated major overhauls. There would be plenty to clarify. Matthew Wong, for instance, came to the U.K. to study dentistry seven years ago. In 2009 he received a post-study work visa and opened a practice in Devon. By 2011 he was qualified for a Tier 1 "highly skilled" work visa. But when he handed in his application last September, there was a problem. "They said that visa didn't exist anymore," Mr. Wong told me. "They weren't clear about it themselves, because if they had been, it wouldn't have taken them four hours to check." Turned out that a Home Office rule-change in April 2011 had closed his Tier 1 category. In fact, as a self-employed dentist, Mr. Wong no longer qualifies for any visa category. The "Exceptional Talent Scheme" was meant to replace the old Tier 1. But it's limited to 1,000 places for foreign experts who have been nominated by Britain's national arts and science bodies. Mr. Wong can also forget the Tier 2 category for immigrants who are merely "skilled," which is now capped at 20,700 places. To be eligible, foreigners must have a job offer from an employer and earn less than Â£150,000. Higher brackets and entrepreneurs need not apply. "I pay my earnings back in taxes and I'm not claiming benefits," protests Mr. Wong, who is now challenging his case in court. "If I had decided to apply for that visa before April , I would have been fine. It's just so arbitrary." The Cameron government has also abolished post-study work visas and introduced annual limits on the number of workers that businesses may hire from abroad. Though international students contribute an estimated Â£9 billion annually to the U.K. economy, they too face new restrictions. It's also built on the last government's "points" system, which grades migrants by the wealth and skills they bring to Britain. Those who arrive without much to their names are denied even the chance to improve their lot. Westminster is now tackling family migration. In June the Home Office introduced a minimum income-threshold of Â£18,600 for residents wishing to sponsor a foreign partner in Britain. The floor rises by Â£2,400 for each child and would prevent about 70% of current migrants from bringing family into the country. There are additional requirements for sponsoring parents and grandparents. Aunts and uncles have been barred altogether. Prime Minister Cameron lobbied for the clampdown in a speech last October, arguing that family-migrant sponsors earning less than Â£20,000 pose "an obvious risk" of becoming "a significant burden on the welfare system and the taxpayer." But if low-earning migrants threaten the British fisc, then so does more than half the British citizen work force. In 2009-10, the U.K.'s median income was Â£19,600. The benefit-scrounger description might be a better fit for native-born citizens, if anyone, given that foreigners are proportionally more likely to contribute more than they consume. The most recent research from the Home Office estimates that while immigrants' taxes comprise about 10% of total government revenue, they take up only 9% of spending on schools, hospitals and benefits. And immigrants don't appear especially keen for life on the dole. In 2002 Britain passed a law that bars asylum-seekers from working before their asylum status is granted. At the time, asylum-seekers made up 49% of net migrants. The law trapped many of them as welfare-claimants for months or even years. By 2010 asylum-seekers had fallen to 4%, according to Oxford University's Migration Observatory. That's not surprising. It's hard to imagine my grandfather coming to Britain if it had meant mandatory unemployment. Were he denied asylum status today, he would need to somehow already have a job earning at least Â£23,400 to keep his wife and children in the country. Britain continues to attract foreigners who are determined to advance through hard work and talent and give back to society. But all residents' fortunes increasingly depend on political whim. The government obsesses over what Britain does for immigrants. A more useful question might be what immigrants could do for Britain, if the government allowed them.