Mr Narrow is correct.
The issue, though, is that the Revenues in various countries see people and companies as individuals, and as none of this has been found to be "crime", yet, then each Revenue/employer/individual solution works just for one individual.
In the UK, whilst the "substitute someone else to do the work" test is critical, HMRC have ducked out of testing this too hard in the IT sector.
It is the IT sector that sets the rules in the UK - not aviation.