It's in their year end accounts under heading "Average Balance Sheets and Interest Rates". You look for the average rate for total average liabilities.
For 2011 it was 2.3% (page 401 of their 2011 accounts)
For 2012 it was 2.2%
For 2013 it was 1.7%
For 2014 it was 1.3%
For 2015 it was 0.9%
For 2016 it was 0.7%
For 2017 it was 0.4%
There are a couple of arguments they might make against using these figures but none of them really hold any water:
- The more relevant COF rate is the "average rate for interest earning liabilities". Well, that's horse crap, as (i) there's little difference between the two, and (ii) non-interest paying customer accounts are a core part of retail banking & retail funding and profits.
- There needs to be a return on equity/capital and AIB was carrying excess capital at the time. Well, (i) the reason it was carrying excess capital was to cover losses so the capital should've been reduced to a pro forma going concern level, (ii) their argument here is further hampered by the fact that part of their IPO price included an adjustment for excess capital which they intended to return to shareholders (so the excess capital was only temporary).
- A tracker opens them up to interest rate risk which they need to price against. (i) then they shouldn't have offered trackers in the first place. And, (ii) if they want to make that argument they need to provide estimates of the cost of an associated basis swap. I think they would also need to show that they sought to hedge the remainder of their "regular" tracker books or it wasn't a genuine risk they didn't expect to just trade through.
Overall, the most important counter to their argument is the fact that
- They had/have complete pricing power over their SVR mortgage rate,
- Since 2008, AIB's SVR mortgage rate never increased beyond 4.4% (in 2011 it was 3%) (per last post in this thread - https://www.askaboutmoney.com/threads/history-of-aib-standard-variable-mortgage-rate.202173/)