When you say "the ability of the bank" are you referring to the term in the contract that reserves this discretion to the bank?
If you are, then your argument is really that the contract term is unfair within the meaning of the regulations implementing the Unfair Contract Terms Directive. That's a legal interpretation and, no, the Courts would not defer to any determination of the FSO in this regard in any appeal.
If you are, then your argument is really that the contract term is unfair within the meaning of the regulations implementing the Unfair Contract Terms Directive. That's a legal interpretation and, no, the Courts would not defer to any determination of the FSO in this regard in any appeal.