The vessel installing foundations for Iberdrola’s €2.4bn ($2.9bn) Saint-Brieuc project off Brittany returned to its home port as officials investigated an oil spillage and the nation’s energy minister demanded answers, in the latest setback to a French offshore wind programme already plagued by regulatory delays and furious protests.

The Aeolus, owned by contractor Van Oord, returned to the Netherlands as maritime authorities probed “an accidental release of hydraulic oil” into the Bay of Saint-Brieuc.