Corporate broking is about the closest that investment banks and their clients get to a state of marriage. The relationships are long-standing, sometimes even life-long, unnaturally close, and, when they work, can be rewarding for both sides. But, as with marriage, divorce rates are on the rise.

This month Dresdner Kleinwort, which used to be one of the top brokers in the City of London, served a decree nisi on as many as 70 of its corporate broking clients when it announced it would largely cease to research or trade in the shares of non-German companies.