While Britain’s other major parties back a minimum wage hike, it is Conservative support that is most surprising. Just 15 years ago, Conservatives vigorously opposed the very creation of a minimum wage. Just last autumn, they balked at pleas for a substantial increase. But this month, the nation’s top economic official—known as the austerity chancellor for his cheerless calls to cut budgets and benefits—startled the political establishment by declaring that it is time to spread the wealth. …