This was taken from the CAB advice site.....
National insurance credits
National insurance credits are Class 1 contributions which you do not pay for. Credits are added to your contribution record when you are unemployed or incapable of work, and in some other situations where you are not working for particular reasons. They will not be paid automatically unless HMRC about your circumstances - for example, you must be signing on with the jobcentre, or have a medical certificate. For some types of credits, you also have to apply in writing.
You get credits when you are 16 for the first three years of your contribution record if your record would otherwise be insufficient. You may also be entitled to credits for years in which you are in training or education. You can get credits for weeks doing jury service, weeks in which you get carer�s allowance, and for weeks in which you get Statutory Maternity Pay or Statutory Adoption Pay.
If you are a man aged 60 to 65 and you are not paying contributions on earnings (because, for example, you have taken early retirement), you will get NI credits.
National insurance credits will not help you to qualify for all benefits.
The rules about when you get credits and when you have to apply for them are very complicated. If you have a query about national insurance credits you should consult an experienced adviser, for example, at a Citizens Advice Bureau.