Some professions (eg nurses working through nursing banks) have case law to define their employment status, but the IT and engineering industries have none.

Case law on employment status does not apply only in the industries where particular cases have been taken: it establishes principles that apply in all industries. Those principles are applied in every case, to nurses in the same way as to IT professionals. So a nurse has no more certainty, and no less, than any other worker. The principles are explained on the HMRC website.