Sorry, just to clarify I should have said if you have a residence order in your favour the court may order an individual you appoint in your will to be the child�s guardian and they would automatically acquire parental responsibility.
s5(1) "Where an application with respect to a child is made to the court by any individual, the court may by order appoint that individual to be the child�s guardian if�
(a) the child has no parent with parental responsibility for him; or
(b) a residence order has been made with respect to the child in favour of a parent or guardian of his who has died while the order was in force."
s5(5) Refers to appointment made by will
s5(6) "A person appointed as a child�s guardian under this section shall have parental responsibility for the child concerned.
(7) Where�
(a) on the death of any person making an appointment under subsection (3) or (4), the child concerned has no parent with parental responsibility for him; or
(b) immediately before the death of any person making such an appointment, a residence order in his favour was in force with respect to the child, "
http://www.opsi.gov.uk/acts/acts1989/ukpga_198 90041_en_2#pt1-l1g5