So we know “Defined Cost is the amount of payments due to Subcontractors for work which is subcontracted”
So are “payments due to Subcontractors” simply what the Contractor has assessed and certified, and is thereby due to the Subcontractor?
As the Employer, what happens if you don’t agree with that assessment? Can you make your own assessment of the Contractor’s certified sum to his Subcontractor?
From your question I can assume that you are using NEC3 and have a Main Option C, D or E, because of the definition of Defined Cost.
Payments to Subcontractors should be made in accordance with the terms and conditions of the Subcontract. Where this is not the case then this is a Disallowed Cost under the 2nd bullet point of clause 11.2 (25).
Any Disallowed Cost is valued by the Project Manager when assessing an amount due under core clause 5.