This is nothing new. We've always been "opted out" of the second state pension(SERPS/Additional State Pension). There's no date on this document, but it mentions a State Pension of £107, so it's some time ago.
https://www.ctp.org.uk/assets/document/417241
Also mentioned here on page 2:
AFPS contracted out from State Earnings Related Pension Scheme (SERPS)
https://equiniti.com/media/792325/20...newsletter.pdf
and here, in 2014:
I served my country but I've been told I won't get full state pension | This is Money