In reply to Sl@te Head:
Do a cash flow budget until you are say 102.
Find out what you spend your money on in a year.
Predict future state pension and other pensions savings etc. Take a stab at inflation, your guess is as good as any.
For planning, 3 stages to retirement, active, passive and doddery. Different income requirements for each, you decide.
Once you have done all that, plug in doing a couple of days work a week until you are 70, it makes a massive difference.