It always was supposed to depend on your National Insurance record, but unfortunately some of the records were lost - they don't admit this but a bank manager confirmed that it is true, when I mentioned it.
They tried to pay me only about half what I as entitled to because they didn't have full records of my payments but fortunately I had asked them for a pension forecast some ten years earlier, which proved that I was/am entitled to the full state pension. It goes up by several pounds a year (about enough each week to buy a pint).
I think the teensy-weensy increase Sen mentioned is the extra top-up they give you if you are over 80 (that's something to look forward to, isn't it).