To be honest for instructors pay it doesn't actually pay for you to be classed as self employed.
It used to work out at something like 29k as a IT consulatant to be worth the hassel. Basically once your on 40% tax it is worth it.
The employeers will say you get to claim x y Z back.
Medical: its reqired to do your job its thier problem they should pay for it.
License: if you go over 3 years again its not a valid reason for them to get shot of you its their problem. Its thier cost not yours.
By being self employed they are trying to get round employemnt law on minimum wages and also you ability to go to tribunal if they sack you because they feel like it.
If you work day in day out in the same place. There won't be a problem you will be under IR35 as an employee.
Basically if anyone refuses to take you on because you don't want to be self emploryed i would shop the buggers to the IR. Its going to cost them heaps in accountancy fees and bull!!!! factor to get the IR to leave them alone.
The advantages more than outway the advantages to an instructor getting payed under 12k a year