It’s Christmastime on Oxford Street. Brilliant displays of white lights rain from above. Decked-out shoppers dash from one gaudy sale to the next. And Johnny Conquest breathes in poison. “The air is horrible. The taxis stop right here, and when they take off, boom, you can taste it,” says the 67-year-old as the heavenly smell of the caramel peanuts he hawks from a humble street stall mingles with the sickly stench of diesel. “I’m on the worst corner in London.” In at least one important respect, it may be the worst in the world. London has come a long way since the days when its infamous coal-fired pollution shrouded Sherlock in a permanent haze or struck at least 4,000 residents dead in less than a week. But the city’s overreliance on diesel-powered vehicles […]