NEC4 Defined Cost: Why the Burden of Proof Sits With the Contractor
Ask ten commercial teams who must prove that a cost qualifies as Defined Cost under NEC4, and you will hear several answers. Too many contractors submit an application, then wait for the client’s cost assurers to decide whether the data is good enough. That sequence inverts the contract.
Project Managers assess the Price for Work Done to Date. Contractors supply the evidence that supports it. Yet client-engaged cost assurers are routinely asked to decide whether the burden of proof has been met, which often means they build the case the contractor should have made.
This is the most common misreading in the cost assurance process, and it costs programmes time, money and trust. Here is how to put accountability back where the contract placed it.
Discover: where the burden sits
Under Options C, D and E, Defined Cost is the cost of the components in the Schedule of Cost Components, less Disallowed Cost (NEC, 2017, clause 11.2(24)). Disallowed Cost includes cost not able to be justified by the Contractor’s accounts and records (clause 11.2(26)). Clause 52.2 requires the Contractor to keep accounts of payments of Defined Cost and proof that those payments were made, and the Schedule of Cost Components reimburses paid cost, not accruals. The Project Manager assesses the amount due (clause 50). The wording is plain: the Contractor justifies, and the Project Manager assesses the evidence offered.
Courts apply the ordinary civil rule: whoever asserts must prove, on the balance of probabilities. The Channel Tunnel Rail Link dispute in Costain Ltd v Bechtel Ltd shows the Project Manager’s side of the bargain: the court accepted it was properly arguable that a Project Manager must act impartially when assessing and disallowing cost (Costain Ltd v Bechtel Ltd, 2005; Gould, 2015). Impartial assessment needs evidence to assess, and the contract makes the Contractor accountable for supplying it.
Diagnose: why the confusion persists
Three habits blur accountability:
• Contractors tend to treat submission as the end of their duty, not the start of their evidential obligation.
• Project Managers ask cost assurers for a pass or fail verdict, when assurers should report findings.
• Cost assurers inherit incomplete data and fill the gaps by investigation, which quietly moves the burden to the client.
The root cause is rarely bad faith. Nobody agreed the evidential standard at the start.
The standard itself is workable. The contractor does not need forensic perfection. It must show, on the balance of probabilities, that the cost was incurred and falls within the Schedule of Cost Components.
Design: set the standard before the first payment
As recommended in NEC4: The role of the Project Manager, agree a cost evidence protocol in the first assessment cycle and write it into the cost assurance plan: that’s a quality plan document. A workable protocol states:
• the evidence of payment for each Schedule of Cost Components item, such as timesheets, payslips, supplier invoices and bank statements, with any extra records the Scope requires
• the audit trail from ledger entry to application line
• who certifies data completeness before submission
• how exceptions are reported and closed
Use data-driven insights to test samples and anomalies, not to rebuild the contractor’s records.
Deliver: hold the line each period
Apply a quality gate to every application. If the data passes, assurers test it and report. If it fails, return it to the contractor with the specific gap identified. The Project Manager then assesses the evidence provided. Assurers advise; they do not author the contractor’s case.
The result is a shorter assessment cycle, fewer disputes and tangible outcomes for both parties: confidence that payment reflects proven cost, and continuous improvement in data quality.
What to do next
Contractors: own the quality of your cost data and the proof behind it. Clients: stop asking your assurers to prove the contractor’s case. Both: agree the evidential standard before the first application.
Test your current process this month. Black Pear Advisory offers a short cost assurance health check for NEC4 programmes. Contact Dr Martin Perks to book one.
References
Costain Ltd v Bechtel Ltd [2005] EWHC 1018 (TCC).
Gould, N. (2015) NEC contracts: programming, project management and pricing. SCL Paper D177. London: Fenwick Elliott LLP. Available at: https://www.fenwickelliott.com/sites/default/files/scl_d177_gould_jan15.pdf (Accessed: 28 October 2026).
NEC (2017) NEC4 Engineering and Construction Contract. London: Thomas Telford Ltd (NEC).
NEC (2026) Assuring people costs under NEC4 contracts: Q&A. Available at: https://www.neccontract.com/getmedia/c6f5e3b5-6d66-47d2-a0ce-6700e9200ef8/Assuring-People-Costs-Under-NEC4-Contracts-Q-n-A.pdf (Accessed: 28 October 2026).
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