You are going to have to talk to a family lawyer about what the legal situation. In the US you would be the legal father as you are on the birth certificate. However, I don't know the law for England. My guess is you have good standing if something happened. A lawyer would be able to give you better advice. If you are thinking about death (and not that mom would leave your relationship with her) then if you are concerned talk to a lawyer and she could also back up you having the kid by putting it in her will or other legal documentation that you are to have custody of the child. If you are concerned about her leaving your relationship then it is you talking to a lawyer to find out what your legal standing is. Good luck.