ZebUK, yours is a different question, but one which is straight-forward to answer.
If you have gaps in your 'contribution years', it is standard practice for the NI Contributions people to write to you, advising that you are missing individual weeks within a particular year, and would you like to make up the missing amounts so that year will 'count'.
What they don't tell you is that you only need 30 complete years for a full Basic Pension, and with the rise in state pension age there are an awful lot of people who are going to have to keep working for longer.
All you need to do is work out for yourself how many complete years you will have by the time you reach 60. You will automatically get credits for the 5 (or more) years once you reach 60 until you reach 65 (or higher) when you get our state pension paid.
But as NJ has correctly pointed out, people with even the full basic state pension get their earnings brought up to a higher figure - so any missing weeks may be irrelevant anyway.
As I said earlier, its a barking mad system.
Provided the magic number will reach 30 by your state retirement age, you are home and dry. There is absolutely no danger that the 30 required years will be increased back up again - there would be a public outcry.