It's taken me 5 years to get round to doing this so if you're a lazy arse poker bum like myself here is a simple guide how to do it.
Firstly you should go here
https://secure.thepensionservice.gov.uk/statepensionforecast/ and get a pension forecast. They have to send you some activation code, just fill in your details and they send it to you in a few days time.
Once you have that log in and it will tell you how many qualifying years you have. To get a full state pension you need to pay National Insurance contributions for 30 years. I checked mine today and it tells me I have paid for 13 years which is pretty sweet imo I had thought it was about 8 but anyway I need to pay for another 17 years LDO to get the full monty £90ish a week pension at todays prices.
They are saying that I can if I wish pay for 3 missing years 2005-2007 which would cost me £1200 but as I'm 37 I still have plenty of time to pay the 17 years so I'm not going to pay the missing years instead I'm going to pay Class 3 voluntary contributions either for the next 17 years or until I (hopefully never) have to get a job. There has been a lot on the news about these missing years. Up until April 5th Class 3 contributions are around £400 a year. They are going up to around £600 a year so if you want to pay the missing years now is the time to do it. It tells you on the forecast where to send the cheque.
One thing I had to think about was if it is better to pay the 3 (cheaper) missing years and then pay voluntarily for 14 instead of 17 (more expensive) years. I think as it's poss I may have to get a job at some point and they will automatically take NI out of my pay packet it would be silly to splash out now and in the future as well so I have decided not to. If this is a mistake plz tell me.
How do you pay voluntary contributions? The easiest way seems to me to fill out this form
http://www.hmrc.gov.uk/nic/ca5603.pdfI don't know if they accept a print out off the internet and my ink has run out so I rang 0845 915 5996 and asked them to send me the form in the post.
So if like me you're thinking "oh noes it's all too complicated I'll worry about it next year" i hope this is some help

I've just reread this and TBH I'm not sure if you have to pay by April 5th to get the cheaper rate for your previous years. There was a big hoo haa about it on the telly but it seems strange that they can put the price up for past years. My forecast says I have up to 2012 to pay for 2005 2013 to pay for 2006 etc so I don't know if from next month those prices jump 50% or not. If they don't and I feel like I want to pay them then it makes sense to do that as late as poss I guess.