There was no legal requirement to preserve pensions for pension members prior to 1991 (pre Pensions Act).
The scheme itself may have allowed it in its rules. I am surprised a scheme the size of Bank of Ireland's wouldn't have had such a rule. You may not have been allowed a pension at the time as maybe you were under 50 or early retirements were not allowed. It would be worth checking to see if you have an entitlement at age 60 or 65 depending on the scheme retirement age.
With regard to the imposition of contributions - this is allowed, but generally with member agreement i.e. I don't think it can be imposed unilaterally. Normally you would be given an opportunity to agree, but that said, if you don't, you will more than likely end up on a lower scale of benefits for future accrual e.g 1/80ths instead of 1/60ths.
I would expect many more schemes to introduce or increase contributions to try and get schemes back to some level of normal funding.