Pension rules are unfortunately a moving goalpost; the rules in 10 or 20 years time are unlikely to be the same as those today. However, major changes were made in April 2006 (referred to as 'A' day) which should hopefully pave the way for some continuity going forward. More recent changes to be aware of include:
State Pension Age
The women's state pension age will rise to 65 by November 2018. Men and women's pension age will then rise to 68 by 2046. There are also tentative plans to introduce a flat state pension for all.
You no longer have to buy an annuity with your pension by age 75. You can instead leave the money invested and continue to draw an income.
Contracted out pensions
If you've contracted out of SERPS/S2P then you can transfer this pension into a SIPP.