CSR could be forced to hand over sensitive internal documents and board papers amid claims from a major customer that the building materials giant used its market dominance to gouge suppliers with “extraordinary” price increases.

Insulation distributor Consolidated Energy – controlled by the widow of the late construction tycoon Len Buckeridge and her son – wants to see the documents to determine whether it can prove CSR misused its market power when selling its popular Bradford Insulation product, which it distributes to suppliers and also installs.