I changed my name to Mums maiden name whenI was younger. We never had to get anything from my dad to let us do it, he is on my birth certificate. I changed what I went by at school when I was about 13 & then when I was 16 I changed it legally. My birth certificate now has my mums maiden name as my name from birth.
All we did was take in a letter from the school saying this is what I have been known by. Plus fill out the forms & pay the fee. Done.