My answer is based on the old pension scheme and it assumes you left after completing 22 years.
Pension increases are only paid once you turn 55, if you left at 40 then your pension remains fixed until you turn 55 at which point it will increase taking into account all the yearly increases since you left.
For example - Leave at 40 with a Â£9k pension. You will receive Â£9k every year until you turn 55. At 55 the new pension is the original Â£9k plus the annual increases over the last 15 years.