Future congrats on name change

I'm not in UK so I can't really help, sorry.
I do understand where you're coming from though. Thought I was going to have the same problem. Still might with a few places... I've not finished changing over everything yet!
I've been asking about titles when doing changes. Sucks to out yourself to so many people - but honestly - they're going figure it out when they see your papers anyway.
Most government institutions over here do not use honorific titles, and those that did allowed me to remove them (I could either remove or use female ones - Mr is not an option until gender marker changed).
Removal of honorific titles was not something that I was told about (even after requesting a title change that they said they couldn't do) - it's an option I had to specifically ask for.
Sure, they're probably still on the computer along with a gender marker - but at least I don't have to actually see them.
Maybe you could try requesting something similar? I know it's a long shot, but here's hoping for you anyway.