By Lucy Kenningham In England and across the world, mayors have wildly disparate powers. So how do they stack up? Lucy Kenningham explains In 1990, Michael Heseltine came back from a trip to Japan absolutely buzzing. It wasn’t the architecture or the sushi. Mayors, he enthused. The UK could do with its own crop of those. John Major was keen, but it was a devolution-inspired New Labour that took the idea and ran with it. Along with rolling out legislatures in Scotland and Wales, Tony Blair’s government created the position of London mayor in 2000. They would have gone further, creating mayors a…