How does my long term partner gain parental responsibility over his children?

How does my long term partner gain parental responsibility over his children?

Assuming he's not on the birth certificate of the child born after the first of December, 2003, in which he would automatically have parental responsibilities, marrying the child's natural mother, having a parental responsibility agreement executed between the two of them would be another way of doing it, or alternatively an application to the court for a parental responsibility order.