There are lot of things you need to create a successful economic centre. Skilled workers are crucial. Stable government helps. So does a reliable fair system, low and predictable taxes, a vibrant cultural life, and a network of businesses that feed off one another. But there is one other factor that shouldn’t be over-looked. As with so much else in life, a bit of luck helps as well.

Right now, it looks like the City just got a break. The crisis at Deutsche Bank could not have come at a better time. In the wake of Brexit, London’s financial centre faced what was certainly its greatest challenge in the last four decades. Both Paris and, more importantly, Frankfurt were determined to steal much...