I never changed my birth certificate. The waiting list is now at 18 months. When someone needs to see it (very rarely), I show them that and the Legal Name Change order from the court. Wouldn't that suffice for the pension forms?
I get the long hassle of changing the BC, and that is why I never bothered. But do you need to?
I guess my point is that I had to describe in court why I was changing my name, provide letters, etc. and the court approved the petition. So it is done. No bureaucrat outranks the judge. They have to accept that I have changed my name and I don't need to explain to them why I did it. Talk to the judge. If they say they need proof of who I am, I present government-issued photo IDs that were given using the BC and Name Change Order.
I know things work differently "across the pond". That is why I am asking.
Hugs!