How do you know what the rates are?
I suspect you get an idea from the experts in SHQ.
Bugger............ they are all sacked.
Seriously this is my biggest worry. Without support from the 'Experts' whom do we turn to for advice/ guidance on what we are entitled to claim? I suspect the answer will be to look at some AP. Having done this in the past I have found that APs were open to interpritation and or subjected to some change hidden away in a DCI or pamphlet, which was not widely distributed.
A real trap for the inocent mistake.