Hi www traveller, It's all about the money right? I agree, i's a shame BASSA don't get it.
Your basic will be unchanged, the MTP is gross of tax I'm sure and it looks to me as if dividing by 12 is how to get its monthly value. (£673.75).
Remember this is paid even when on leave/SEP/sick. I suggest you look back through your pay slips and see how this compares to your earnings over say 24 months to get a good average.
Also thanks to the tax mans recent grab on allowances getting this included as a fixed payment does not increase your tax liability.
Finally the MTP does not cover all your payments. The following list of payments will still be paid as before, so don't forget to leave them out of your average payment calculation.
Meal Allowances Daily Overseas Allowance (DOA)
Nightly Incidental Allowance (NIA) Time Away Allowance (TAA)
Line Trainer Payments Willing to work
Rest Day Working
Exceptional Payments from WW Disruption Agreement (One-Down and Zone
Closure).
HTH