Errr, another quickie chaps....
My NI record shows 33 years. I know for a fact that I never paid NI on my part time job while I was at school. As nobody knew about it 
But for 2 years, whilst still at school, I have 52 weeks of NI credits each year?
Is that correct?
Specifically, for the 2 years in question, it says this...
National Insurance credits: 52 weeks
These may have been added to your record if you were ill/disabled, unemployed, caring for someone full-time or on jury service.
Everyone gets credited for the two years that they were 17 and 18 and in full time education or training.
The 33/35 year think is only correct for people who commenced NI payments after 2016. You started before 2016 so chances are you won't need 33/35 years to achieve the £168 total. Infact, from what you're saying you are already there, and any future NI payments won't increase your SP.
Thanks!
So no matter what I do, I cannot improve it, except by deferring.
Assuming I'm not working at 67, can I still defer? Is there any benefit, or just bank/invest it, all assuming I am comfortable on any potential drawdowns from one of the private ones?
You can't defer it until you actually reach your SP age - 67 or 68 currently depending on your DoB. You don't have to be working at 67/68 to defer, and yes you can defer SP and drawdown from your private pensions at the same time. The deferral rate used to be 10%, which was incredibly good value, but was changed to 5% when the new SP was introduced in 2016. The 5% increase is as cast iron a guarantee as you'll find because it's backed by HMG. You can probably beat 5% with conventional investment returns, but these also carry risk - you could lose the lot should an investment go bad. You can't lose your SP (Marxist governments or global apocalypse excepted).
The biggest risk with deferral is probably death. You have to live long enough collecting your enhanced SP to claim the money that you would have got if you hadn't deferred. There are also tax implications. Despite what most people think the SP is taxed - they just reduce your personal allowance (tax code) by the amount of your SP. That means you pay more tax on any other private pensions you have. Deferring SP can allow you to drawdown more of your private pensions paying less tax in the 55->70 age range and then when you start taking your SP it's 15% bigger than it would have been, with no investment risk.
