The head of the Nigerian government’s Debt Management Office is as mild-mannered as debt management officers come. But even he could not resist what in that profession must be the equivalent of a sportsman’s victory dance: a flourish to demonstrate the consummate mastery of his game.

Into his PowerPoint slide presentation detailing Nigeria’s clearance of more than $30bn (£15bn, €23bn) of its external debt, Mansur Muhtar, the official, slipped an unexpected but dazzling image of fireworks.