London does not need a mayor; it needs a prime minister. Britain is fracturing. Scotland may yet quit the union and England turn its back on Europe. The Conservatives are throwing up barricades against the immigrants who are the capital’s lifeblood. The world’s most vibrant capital city cannot entrust its fate to a little England. This is a moment to imagine a different future: independence.

Boris Johnson, the present mayor, says he too wants power shifted from Westminster to City Hall. His demands — for a tad more financial autonomy and oversight of the courts — are piffling. Unsurprisingly so. Mr Johnson will soon vacate City Hall for the House of Commons. He aches to replace David Cameron in Downing Street. Mr Johnson’s loyalties to London count for nothing against consuming ambition.

The economics of independence speak for themselves. With a population of 8.5m (closer to 13.5m in the wider metropolitan area) London accounts for more than a fifth of Britain’s gross domestic product and generates as big a chunk of its tax revenues. This gives it an economy about the size of Sweden. Unemployment is less than 3 per cent; the demographic profile is more youthful than in the rest of the UK. Tourists spend ￡20bn each year in the capital.