On the job advert it says 'main scale' in the pay category. I'm currently on upper 1. I'd love the job and wouldn't be bothered about being put back on M6 if it would help me get the job. I'm teaching on a 0.4 contract at the moment and this is for 0.8 so I'd be taking home much more anyway.
Confusing thing is, on the application form there's a section saying- illustrate how your experience meets the threshold criteria of the school - (relevant only if the post for which you are applying sits on the Upper Pay Range).
Should I leave this blank? Or fill it in as I do have decent stuff to put in there, subject leadership, extracurricular clubs, leading assemblies, trips, concerts etc.
Fill it in - it sounds like you have plenty of relevant experience. Now that pay portability has gone they might not offer you UPS1 but as cynderella says I would also interpret 'mainscale' as 'not on the leadership spine'.