Did you commute any of your pension? If so the increase could be large. However weren't you briefed by your PD clerk just prior to discharge? I was informed in writing what the commutation would involve, I therefore knew what was headed my way at 55.
The thread below has a link to a multiplier table, find the row with the date range applicable to your leaving date in column A and multiply your full Pension (the amount you would have got if you did not take commutation) by the figure in column D. This gives you the amount you would get if you were 55 this year. http://www.arrse.co.uk/community/threads/2014-pension-multiplier-rates.210495/
There is another thread on here somewhere with a table that you can plug the RPI (now CPI) figures into to give you a good idea what the increase should be. I'll have a dig around and post the link in a bit.