I was in, out, shake it all about in the past. Don't know if that's made things better or worse, but cant change it now, so no use fretting.
Well I've heard you can buy years, but when I rang 'em they said that wouldn't apply to me 
It all changed on April 6th 2016. Long story short - providing you have at least 8 working years after April 6th 2016 in which you have/will pay NI, and you end up with 40 or more years, then you will qualify for the maximum new state pension amount - currently £168.60 per week.
The money paid into your 'opted out' fund will be in addition to this. For the vast majority of people 'contracting out' of SERPS has turned out to be a very, very good idea - admittedly only realised in hindsight.
Thankyou for that. So to clarify in my head, if I started work Sep 1988, and was contracted out of SERPS, for a long period. I will get the full state pension if I work and pay NI until Sep 2028?
If I don't pay NI for any reason until then (assuming I stop work in 2028 or earlier), some pro rata calculation is made?