I rather think that the predictions mentioned in the previous post are based on a much larger fall in staff numbers over the next half-century, accompanied by an increase in the cost of the pensions for them.
Forecasting minutiae like the tally of Civil Servants in 2060 in 2011 makes no more sense than forecasting the 2011 establishment in 1962.
Forecasting annual pension costs in 2060 is fatuous.