I would argue it is not that simple. The prevailing rate will be different for different people. For me, I was on ECB + 0.75%. My "prevailing rate" should always be ECB + 0.75%.Just be careful over-estimating the money back.
1 - they will need to work out the correct or most apt margin. This will probably be the highest of the margins they had generally available. - Possibly as high as 2% and unlikely to be under 1.5%
As per the definition of a tracker rate, and to quote AIB's own terminology:
"the Margin/Adjustment above the ECB rate, this will stay static throughout the life of the loan."
Therefore, it is the margin on the day the mortgage loan started. After that, the prevailing rate is the margin + whatever the ECB rate is (the variable component of the prevailing rate).
I certainly won't be settling for anything less.