Does British Telecom pay more or less to its company pension scheme members depending on whether they are contracted in or out? Or have I missed the point altogether?
I can't speak for BT, but...
...the railway pension is a salary sacrifice final salary pension. Until April this year the (contracted out) sacrifice was 10.64% of (basic salary)-(state pension).
Fom April onwards it was decided that as employees would pay more NI the sacrifice would be reduced to circa 8.5% (I don't have the exact figures to hand).
The rail pension is payable at (final salary-1.5x(state pension))x(years accrued*/60). The reduced sacrifice will supposedly match the reduced railway pension with the increased state pension to give an overall (rail plus state) pension of a similar amount for any given wage.
*to a maximum of 40 years
Much like other final salary schemes that changed (AFPS '15 for example), employees will have accrued a guaranteed certain amount before a given date, and will accrue it at a different rate thereafter.