>It's actually down to whether the client wants the work to be done by you personally or your company (and by that it means by anyone your company would provide). If the service provided is personal then in HMRC mind it is in scope...
Interestingly, from my experience over several decades, that still largely applies to contracts with the big integrators, the only advantage the big boys have is a warm feeling that they have the reserves to resolve any delivery problems that may arise...