On the marriage certificate you can only put your fathers name down or leave the box blank. I was raised by my mother and wanted to put her in the box. This is not allowed. FFS it's about time these last vestiges of patriarchy were removed. A parent is a parent.
Also had I been having a civil partneship I could put anyone including a step parent down.
Please write to your MP asking for change, I have and got no joy. Looking for numbers here folks.