Ok you may know this already so just ignore but I'm sharing this because I would have liked this clarified myself by someone who had actually done it. Retired early, took TP and then have a gap till age 66. I could not achieve the full state pension. Was considering paying the £700+ per year to plug the gap. THEN I heard that if you had done exam marking or invigilation you could pay the much cheaper class 2 NICs. Have just spent a profitable hour on the phone to the future pensions Dept and HMRC. Pensions people confirmed how many years I need to pay then told me to ring HMRC to confirm the class 2 NICs. HMRC confirmed I was eligible and registered me as self employed and told me how much I need to pay and when they will bill me each year. Told me to ring pensions back to just check. Did that and a really helpful lady told me exactly how much each year would improve my state pension. Basically each bought year is about £4 a week more. Class 2 contributions are about £156 for the year. A few calculations suggest that if I pay those for 7 years I receive about £30 per week more. I would be better off in less than a year. Currently that is the law and of course could change. At the moment it is a no brainier. You don't have to contribute each year but each one boosts your state pension. The DWP future pensions Dept is 0800 731 0175.