You do not apply WAO to subcontractors. The question really is whether you have a subcontract or a labour only supply contract. If you look at the definition of Subcontractor it covers "construct or install", "provide a service" and "supply plant and materials". Provision of labour only does not, in my view, fall into any of these. It could be argued that the labourers "provide a service" but that is not what the contract is about, the contract is about supplying a person who then carries on work at the direction and under the supervision of others.
Therefore, I disagree, a true labour only, supply, contract would generate WAO.
Therefore, I disagree, a true labour only, supply, contract would generate WAO.