I'm being told they can't pay me until they've been paid

It is one of the oldest lines in construction: the client has not paid us, so we cannot pay you. It sounds reasonable, it buys the payer another month, and it quietly moves their cash flow problem onto your books. Meanwhile your contract is with them, not with whoever sits above them, and your people and suppliers have been paid for the work already done.

The Construction Act took most of the force out of that line years ago. Pay-when-paid clauses are generally ineffective under the Act, with a narrow exception where the party up the chain has become insolvent, and conditional payment terms dressed up in other clothing often fail with them. On contracts the Act covers, your due dates, notice deadlines and the rule that an unanswered application can become payable in full generally continue to apply, subject to the contract, the notices actually served and that insolvency exception.

So the question is rarely whether the excuse is good. It is what your contract and the served notices say this cycle, because that paperwork usually decides who is actually entitled to what, and when.