One more thing I thought I'd mention - back when I started, starting pay was linked to degree class. e.g. all those with 2.1 / first class honours would start higher within the grade. I compared with some friends in my first year and realised I was being paid less - wrote in to HR and realised they hadn't captured my honours class, so they ended up adjusting it (with backpay).

After a few years in service, it'll probably get out of sync since each year's increment is affected by previous year's performance grade.

I have no idea how they decide where to place you within the scale when you get promoted - I imagine there's some formula for it that gives you a bump in salary while keeping some space before hitting the next salary ceiling.