From 6.30pm today the London Underground will grind to a halt for the second time in four weeks. Unions are unhappy about plans for 24-hour services from September, arguing that proposed bonuses, pay rises and working-time arrangements are insufficient. Commuters, walking home or queuing for crammed buses, will curse; and there is talk of yet another stoppage soon. Businesses are also grumbling; July’s strike was estimated to cost London’s economy £300m ($470m). But Londoners should cheer up. At 8.6m the city’s population is higher than ever; daily it inhales 2m commuters, many heading for the financial, technology, law and business-services firms at its heart. Improvements are essential because London is booming; that leaves little room for compromise on the Tube. The industrial action is a symptom not just of the unions’ power and militancy, but also of London’s success.