Are we missing the point?
Why are "self employed" instructors not concerned about this?? If HMRC win against Sherburn it will create a dangerous precedent. In the current economic climate, I can't see Flying Schools being able to pass on the costs of Employers NI to customers without there being a reduction in overall demand for flying training.
Therefore if overall income to Schools is unlikely to grow a newly defined employed instructor can't earn any more. In fact they might earn 12% less to cover the School having to pay Employers NI. So the same pot of earnings we get now is redefined to cover normal pay, holiday pay, sickness pay etc etc.
Perhaps more importantly - I like to manage my own tax affairs. I prefer to deduct my business associated expenses prior to paying tax, and do not want to be in a situation where HMRC can deduct PAYE/NI at source on gross pay and I have to fight to get it back retrospectively.
If HMRC win, I'm not sure I can afford to instruct as I currently do because I'm sure it will mean I'm paid less and taxed more. Perhaps I shouldn't worry then, because if this forces Clubs like Sherburn to decide they can't afford to run a school it will all be outside my control in any case.