I haven't, but I am probably about to. Have already spoken to manager; one of this weekend's tasks is to compose mail for union.
There's some good advice online about chosing comparators and so on. I have it bookmarked at work, but just now, I am on my personal phone on a train. Will do my best to remember to post link when I can check the link.
I was preparing to do this but it got resolved before I got too far.
I first raised with my line manager who basically said it was historic, unfortunate and nothing could immediately be done.
I then raised with HR and asked for more comparators. They took a couple of months to look into it, didn’t provide me any more info but did give me a back dated rise. No admission of the reason being the comparator I originally quoted, they said it was because my area had said a rapid recent rise in market rate and that my pay had used older market data. I chose to leave it there. Not a perfect outcome but I got a good pay rise and my line manager will think twice in future.