The Commission des Opérations de Bourse (COB), the French markets regulator, has intervened in the increasingly bitter battle for control between Kingfisher and Castorama, warning both sides that they must ensure the clarity and fairness of any information they release in the coming weeks.

In a rare intervention by the regulator, Michel Prada, president of the COB, has written to the management of both Kingfisher, the UK retail group, and Castorama, the French DIY group, reminding them of their responsibilities to all shareholders during the bidding process.