Most government pensions are fine income sources! But, many of them do not include inflation adjustments. Make sure to account for inflation in your planning. Find out whether your pension is inflation adjusted.
Illustration: If you retire at 55 and live to be 91, you've got 36 years coming. Inflation at 2%/year would cut the value of the pension in half by then.
No one can be certain of inflation rates, so no one can be sure of how much the reduction will be. But you can estimate. As a crude example, if you estimate that your pension will have an average buying power equal to 2/3 of its original amount, and the original amount is $3000/month after tax, then you would plan on the pension paying for $2000/month of expenses. In the early years of pension draw, you would invest the extra, so that the resulting investments would compensate you during the phase when the pension's buying power drops below $2000.
Are there ways to protect against inflation, instead of just guessing the future amount? My personal theory is that if you're up for it, a mortgage or set of mortgages that are the same size as the pension would shelter it quite nicely. But I've never seen that described by anyone else.