This pension is called the Guaranteed Minimum Pension (GMP).
The Government changed the system from 6 April 1997 when GMPs ceased to accrue.
For contracted-out membership from 6 April 1997 to 5 April 2016, the Actuary has to certify that the level of benefits provided under the Fund overall is at least as valuable as that under contracting-out regulations.
Your Basic State Pension is not affected by being contracted-out.
If you were a contributing member of the Fund for any period between April 1978 and April 1997, your pension may comprise an element of GMP which attracts a different rate of increase once you reach GMP payment age, which is 60 for women and 65 for men.From 6 April 2016, it is no longer possible to contract out of the State Second Pension.