NEC3 ECC: Where in NEC option C, can I establish who holds responsibility for the design? (I.e D&B or Traditional)

We’re about to enter into a Option C contract as the main contractor. The client is providing all the design. Where in the NEC contract is this made completely clear?

in the standard form, clause 21.1 states that the Contractor designs the parts of the works which the works Information states he is to design.

You therefore need to refer to the Works Information for what parts, if any, the Contractor is to design.