For months now, the most useful credit-analysis tool for European investors has been a very simple one: a map. Corporate borrowing costs are being determined almost entirely by where a company happens to be based, even if its businesses are pan-European or global. And some recent bond deals show that the difference between north and south is becoming extreme. Investors weighing up what the European Central Bank will do next should pay attention.

Northern European borrowers are increasingly able to lock in extremely cheap financing - including at negative real rates - while southern companies are left out in the cold. The numbers speak for themselves: German engineering giant Siemens is paying investors a coupon of just 0.375% for a two-year bond, a record low, while Spanish bank Santander had to offer a coupon of 4.375% for the same maturity.