MN1 without father consent

Can I apply for a child's British citizenship (MN1) without father consent?
Background:
- Child is Spanish, born abroad, moved to the UK at 2 weeks old - now 9 years old. Child has settled status, and has lived in UK all his life.
- Mother (original Spanish citizen with settled status in the UK) was granted British citizenship.
- Estranged father, Spanish, lives abroad, and has little contact with child. Father had originally agreed (via email) for the child to apply for British citizenship, but has since changed his mind and refuses to sign consent form (does not have any good reason for objecting to it - just part of his narcissism and coercive behaviour towards me).
- Not sure if it matters, but step-father is British by birth and has parental responsibility.

What should I do? I am afraid that if I apply without father's signature, my application will be rejected and fee is not refundable. Maybe I can say that father can't be contacted, and leave it as that? Maybe I can use the email as proof that he has agreed?

Any advice is greatly appreciated!