I don't think the rule book will shed any light on the subject. Many rule books are similar i.e. your pension will be based on final pensionable salary less x times the state pension.
Rule books were written before the new retirement age was proposed. They are based on the Deed. So unless they Deed was amended for the new retirement legislation then the booklet won't give a definitive answer. This is another grey area in the pensions arena that the Govt has not properly legislated for.
I don't see that the scheme would deduct zero pension in year 1 or 2 until the sate pension becomes payable. Currently, the offset amount is the pension rate ruling at retirement date and is not changed in subsequent yrs when the state pension changes. So I don't see any requirement on the pension fund to change this practice.
Therefore I believe they can legitimately deduct x times the prevailing state pension at retirement date even though the state pension it is not in payment.
But this also brings into question the OP's contractual retirement date - like many contracts of employment it may not state the actual retirement date - often this has been assumed to be the retirement date stated in the pension trust deed or the date of the old age pension. So, OP may be entitled to remain in employment until the state pension is payable.
If employer does not want this then the trade-off may be to supplement the occ pension until the state pension is payable but this may not be feasible due to funding position of the plan. In such case the employer may pay the difference directly.
This whole issue seems to have been kicked to touch and there is little guidance available. But pension funds are not funded to pay for it and this is a problem. Trustees cannot automatically decide to pay it as they may disadvantage the scheme.
It needs proper legislation to cover all the above issues.
I understand Ajapale's point about employers gaining from increased state pensions in recent yrs but an increase in pensions has always been factored into actuarial valuations. While the increase in the state pension during Berties period in office was probably more than this factor, the increase in actual salaries in this period has also been generally more than the assumed salary increase in actuarial valuations. So the implication that employers have some sort of buffer to pay for the state pension delay is not so clear cut.
( I have not been following this area for a while so feel free to correct me on the new retirement age legislation)