s 45 Arrangements with agencies
If— (a) an individual (“the worker”), with a view to personally providing services (which are not excluded services) to another person (“ the client ”), enters into arrangements with a third person ..., and (b) the arrangements are such that the services (if and when they are provided) will be treated for income tax purposes under section 44 as duties of an employment held by the worker ..., any remuneration receivable under or in consequence of the arrangements is to be treated for income tax purposes as earnings from that employment.