British Father refusing to sign child's German passport

[Chrissy_Banana]

My daughter, born in the UK in 2002 to her father (who's British) and me (German and have lived in UK since 1999) needs to get her German passport renewed. Her father is refusing and doesn't get in touch with me over the matter.
I also would like to register as a British citizen but again I can only do that with her having a valid passport.
What is the easiest and most cost effective way to get him to sign her passport application. He's got parental responsibility and according to the German passport application we need both our signature on the document. She would be able to apply for a passport herself in a year when she turns 16 but she was meant to go abroad this summer.
Thanks in advance.

[secret.simon]

I also would like to register as a British citizen but again I can only do that with her having a valid passport.

Do you mean to register her as a British citizen? Were the father and you either married at that time of birth of the child or married subsequently?

[Chrissy_Banana]

Yes, I'd like to register her as a British citizen using form UKF. No, we were never married at any point.

[CR001]

Yes, I'd like to register her as a British citizen using form UKF. No, we were never married at any point.

Do you have proof of his citizenship and passport copy etc to do a UKF application?

[Chrissy_Banana]

I suppose I could order his birth certificate to show that he was born in this country and is British but unfortunately I don't have a copy of his passport and I doubt he'd give me his copy. I could try asking his father though to organise me a copy (he's a bit more reasonable). Would it have to be a notarised copy or would an unnotarised copy do?
Thanks so much for your help.

[Chrissy_Banana]

Can anyone help please?