As part of its understanding pensions series, the BBC News website provides a guide to Serps.
Very low earners have their state second pension topped up
What is it?
The State Earnings Related Pension (Serps) was the name of the government's additional pension scheme until April 2002.
Anyone who was earning more than £75 a week and had not "contracted out" (see below) would have been building up an additional pension under Serps.
It is now called the State Second Pension.
However, people who made contributions before April 2002 will receive an additional pension based on Serps way into the future.
Why did the government replace Serps?
The government replaced Serps with the State Second Pension, because it wanted to give certain disabled people and those with long-term illnesses the chance to benefit from an additional pension scheme.
The new scheme also fits in with the government's political agenda, as it increases support for low to middle income earners.
While the State Second Pension is still related to earnings, people on modest earnings who qualify under the rules are much better off under this system than Serps.
This is because the system "credits" or "bumps up" earnings for eligible groups to a flat rate of £12,100 from 11 April 2005.
In other words, a person contributing to a contracted-out personal pension earning less than £12,100 in a tax year will also get a State Second Pension top-up for that year.
Am I automatically a member?
If you earned enough and paid employees' National Insurance Contributions, you were automatically a member of Serps.
This is known as "contracting in".
Serps was related to earnings, so the amount people will get at state pension age will vary.
Members of qualifying private pension schemes could "contract out" of Serps.
If employees joined a contracted-out occupational pension scheme, they and their employer would pay lower National Insurance contributions.
If you contracted out of Serps using a personal pension plan or a stakeholder pension plan, the Government paid part of your National Insurance contributions into the plan once a year in the form of a rebate.