I think if you work it out you'll find you are being paid the national minimum wage as your retainer, and any flying pay over and above that will put you above the NMW. I know the company you work for and as an employer you can do a lot worse. I left last year and so am not beholden to them and can say what I want which is: the investigation by the IR is unwarranted and will serve no useful purpose except to employ some accountants and investigators for a while. The terms and conditions at the place you work are better than at most other flying schools and if you don't **** people off you will be treated well too. Don't think the IR is any friend of yours - they'll **** up the whole UK flying training system given half a chance and leave instructors with no jobs at all, let alone poorly paid ones.