The school could have employed you for the past 3 years as an unqualified teacher ont he Unqualified Payscale. They could have pitched your pay at the point on that scale that was just under M1 on the qualified scale and you would have progressed up the Unqualified Scale. Then, when you achieved QTS equivalency, you would move to the M point that paid just above your next point on the Unqualified Scale. They could have started you at Pt4 of the Unqualified scale (a few hundred pounds per year less than M1) and you would now be on the top of that scale, pt6 (£25016 p.a in most of England and Wales - higher around London). getting QTS and moving the the qualifed scale would mean starting on the M scale at M3, £25168 (AT LEAST). I'd see about getting the post re-assigned as a teaching role on the unqualifed scale now and try to negotiate at least pt4 on that scale.