When you stop working you will no longer receive a salary and you won't receive state benefits until you are 65 for men, 60 for women (please note that this is changing to age 65 for women gradually between 2010 and 2020). Have you thought about how you will replace your salary? You may have savings or property but will that provide you with the income you desire in retirement?
If your employer offers access to a pension plan, this section will show you some of the benefits of joining.