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How can He find out if He has opted in out of SERP's?
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its not opt out. it is contract out. Opt out means something different (although it is a common error). You havent been able to contract out of SERPS since 2002 as it was abolished back then and replaced with the State Second Pension which itself ended in 2012 for money purchase pensions.
Contracting out is actually a term that covers two very different methods. Both contracted you out of Serps/S2P but what actually happened by contracting out was very different. One method resulted in lower NI being paid and the employer pension effectively making up the difference. The other method resulted in pension fund building up. (highly simplified to keep it short).
It would help if we knew the context of your question. i.e. what is he looking to find out?
I am an Independent Financial Adviser (IFA). Comments are for discussion purposes only. They are not financial advice. If you feel an area discussed may be relevant to you, then please seek advice from an Independent Financial Adviser local to you.