NEC3 ECC: Plant Operator Costs under the SOCC

I have a query relating to how the cost of plant operators should be dealt with under the SOCC, and in particular whether the working area overhead charge applies.

Scenario:

The contract is NEC3 ECC - Option C

Project includes various items of hired plant (excavators, articulated dump trucks,
dozers, etc.) from a number of specialist suppliers which are provided with operators.

The invoices provided to demonstrate the cost of plant show separate line items within each invoice for the equipment and the operator.

The Contractor considers that the plant operators costs should be treated as people under item 14 of the SOCC, and attract the working area overhead percentage addition, on the basis that the cost of the operator is shown as a separate charge.

The Project Manager considers that these costs should be deemed as “operated plant” and costed under SOCC item 21, for which the working area overhead addition does not apply, on the basis that if a particular item of plant was out of action the Contractor would not be paying either the equipment or the operator costs.

Which definition of cost is correct?