I've got a feeling this is for the Army and it's LEs (I stand to be corrected), or maybe Branch Officers...
I was a FS on commissioning and went on to the next highest equivalent officers' pay band (F/L level 4, I think). As I gather, an SAC would normally grad a Fg Off and would go straight onto Band 6 Fg Off pay. eg top rate SAC Tech - £27500 (2008) would go onto Fg Off Band 1 £28200 (though I seem to remember something about there needing to be a 5% increase, in which case he/she would go on to Band 2 Fg Off). In my case, I gradded as a Fg Off and then marked time until I had 4 yrs seniority as a Flt Lt.