If your main contract is let under an Option C, can you let your domestic subcontract packages under Option A & B? What level of evidence do you require to substantiate a final account externally for an Option C? Would the measured works BOQ / CE’s / Final account statement and final payer notification be sufficient? Surely you don’t need to get every invoice for incurred costs from the supply chain for every package?
The short answer is yes you can.
In order to substantiate the Option C Defined Cost you will be required to demonstrate that you have paid the subcontractor in accordance with his subcontract. A copy of the measured works BoQ together with CE assessments should be sufficient to demonstrate the Defined Cost but there may be matters that fall as disallowed cost ie the subcontractor is entitled to payment (therefore Defined Cost) but for which the Contractor is not for one of the reasons set out in clause 11.2(25).