SERPS provided an earnings-related addition to the Basic State Pension paid by the Department for Work and Pensions (DWP).
SERPS additions were based on National Insurance contributions made between 1978 and 2002, with a maximum of 20 years' contributions counting.
Members of the LGPS were automatically contracted-out of SERPS for the duration of their LGPS membership, and this will be taken account of in calculating their "new" (from 2016) state pension.
This scheme replaced SERPS - see State Earnings Related Pension Scheme. S2P was a top-up to the basic state pension until April 2016 and members of the LGPS automatically contracted-out of S2P for the duration of their LGPS membership.