So here I am, minding my own business, anticipating I'll have to ask my employer for an advance when I next go in (long story, but thankfully seems irrelevant now, unless any of you lovely people are going to spoil my day

Having looked at my wage slips, there appear to be massive discrepancies. There is my pay (usually £1900-£2100), but there are a few additional payments for some months ("pensionable payment" and whatnot) for similar amounts. All this has resulted in my wage slip for some months showing up to £6000 gross pay! Even on emergency tax, I still have been receiving £1200-£1300 (after deductions) per month so never thought to double check. So my gross pay for 5 months (not counting the last month) is £17+ thousand.
However (there's always a however), my wage slip does say "payments" which is my actual payment (before any deductions). Will this be used instead of gross pay? Even using this, I still meet the minimum (obviously a lot closer, but I just edge over the requirement when you /6 and x12 even for 5 months).
And another however. The final pay that I'm expecting (and the reason I was planning on speaking to my employer about an advance) should be for april. However, because of a complicated situation which may or may not force me to issue legal proceedings, I don't anticipate receiving very much. It's holiday pay and amounts to less than £100 (it's for 1 of the locations I work at). Will they use this instead for the /6 and x12 as it's the lowest amount I'll have earned in the 6 months I'm using? If so, is there any way around this from what you've read of my situation I.e. applying via a different route etc?
Sorry if I've come across a bit dramatic, but this has really thrown me. Any advice would be much appreciated.