This is the argument which I think is fundamental and which should succeed.
There are other arguments and it would be very helpful if other people made them. It does not matter which argument succeeds as long as one of them succeeds and it applies to everyone in the cohort.
Here are some of the other arguments I have seen
1) In the absence of a prevailing rate, the rate prevailing on drawdown should be used.
2) of course the prevailing rate would be different when the fixed rate ended because the ECB rate would have changed. But the margin prevailing at drawdown would not change. That is what a tracker margin is.
3) AIB should not be allowed to compensate for their breach of contract by making up a prevailing tracker rate 9 years later.
4) The contract is an unfair contract under the EU Unfair Terms and Conditions and so the contract is void.
5) AIB's suggestion that the margin would have been as high as 8% is a joke.
6) The prevailing rate should be the average margin on offer to all existing customers on trackers
This thread is not to discuss these issues. But feel free to discuss them in other threads.
Brendan