British citizenship for 10 year old

A child was born in the UK, however her mother did not have ILR at the time of her birth, but her father is a British citizen. Her father is in prison and does not have access to his birth certificate/passport and we are not in contact with her father. Mother and Father were married at time of birth (but now divorced). I'm assuming the child is a British citizen, but due to the lack of information of the father, how can the mother apply for a British passport for the child?

Thanks.

bump

Was the father born in the UK?

Yes the father was born in the UK.

Then just get a copy of his birth certificate from the GRO.

We're not able to contact the father though, how can we order a birth certificate without him?

Anyone can order a Birth Certificate online (click).

thank you