SERPS, or the State Earnings Related Pension Scheme, was a pension arrangement allowing those who paid full Class 1 National Insurance contributions between 1978 and 2002 to receive an earnings-based pension. It was possible to opt out of SERPS, which was replaced by the Second State Pension in 2002.
It was introduced in the 1970s as a top-up to the basic State Pension, and was later replaced by the State Second Pension. You'd only be eligible for SERPS if you were an employee paying class 1 National Insurance contributions. The amount that you'd get from SERPS would depend on your earnings. Lots of people chose to, or were advised, to opt out of SERPS, and instead their national insurance rebates were paid into a personal pension plan. Many people didn't realise what this meant and as a result have lost track of where their contributions went.