This does depend on how you count. I can’t find the article now, but I did see one saying that the average nurse has had above inflation pay rises over the last decade. The number the union presents is adding up all the cost of living increases, which hasn’t kept up. However nurses, like many other workers, also have their pay progress up the pay scales.
Pay scales, whilst increasing pay for the individual, have limits.
For example the maximum range for a band 6 is about 5% from bottom to top and according to this website you can't have an increase for 2 years:
Pay scales for 2022/23 [Archived]
NHS terms and conditions annual, hourly and HCAS pay values scales for 2022/23
As such someone being promoted 12 years ago to the very bottom of that grade will have only just not seen their pay decrease of they now sit at the very top of that band (assuming a 5% reduction in band pay rates over that 12 year window). However, unless they get a promotion to the next band they are now at the very top of their band and so pay scales won't help.
However for new entrants to a given band they are now being paid less than someone promoted to that grade before them.
Whilst that's going to encourage people to try and move up bands faster.
Have pay brands seen an increase, well according to:
Agenda for Change pay bands | Nursing Times
Pay rates from 1 April 2010 Band 1 Point 1 13,653 Point 2 14,008 Point 3 14,364 Band 2 Point 1 13,653 Point 2 14,008
Band 6 was (lower end) £25,472 putting this through the Bank of England inflation calculator:
This would be worth £36,088 now, rather than £33,706 (lower end) or £35,572 (upper end). As such even someone starting in band 6 in 2010 would, even allowing for them now being at the top end of their pay band, would be about 1.5% worse off in real terms.