Compulsory serps

xylophone

As Hyubh points out, there seems to be a deal of confusion here.

OP, what exactly is shown on your State Pension Forecast?

https://www.gov.uk/check-state-pension

It seems that you will reach SPA in the first few months of next year so may have started building your NI record around 50 years ago.

 With regard to additional state pension, the State Earnings Related Pension Scheme began in 1978 and  was replaced by State Second

Pension in 2002.

S2P ended 5/4/2016 with the inception of New State Pension.

https://en.wikipedia.org/wiki/State_Earnings-Related_Pension_Scheme

https://en.wikipedia.org/wiki/State_Second_Pension

Contracting Out  of SERPS/S2P ended for Defined Contribution Schemes 5/4/ 2012 and for  Defined Benefit Schemes on 5/4/2016.

https://techzone.aberdeenadviser.com/public/pensions/Tech-guide-contracting-out

You say that you elected not to join your current employer's pension scheme when you started this job back in 2005. At that point in

time, joining such a scheme was not a condition of employment.

Did you set up a personal pension of some kind?  Or you were just contracted in to SERPS?

Automatic enrolment    https://www.moneyhelper.org.uk/en/pensions-and-retirement/pensions-basics/automatic-enrolment-an-

introduction was gradually introduced from 2012 but an employee could choose not to join - presumably you chose not to join.

Could you clarify your position having read through the links?