When I was born, I was given my father’s surname. When I was seven, I asked my mum why I didn’t have the same surname as her and my sister (who both have my mum’s ex husband & my sister’s dad’s name, which is why it wasn’t originally given to me) as our household consisted of only the three of us, and at the time we were not in contact with my father. We changed my surname to a double barrel so I still had my father’s name, but also the name my mum and sister used. As far as I’m aware, my mum did not need my father’s permission to do this, but she did need a witness to the name change (her own mother, my grandmother, did this).
I’m happy with my double surname. In fact, it’s quite useful, as I can legally use just one or the other if I wish, as the legal documentation does not include a hyphen between the surnames.
Just thought I’d input from a different perspective!