�If the mother and father were married at the time of the child�s birth, or they have married subsequently, the father will share parental responsibility for the child. For births registered on or after the 1st of December in 2003, an unmarried father automatically acquires parental responsibility if he is recorded as the child�s father on the birth certificate.�
Source: The Deed Poll Service �
http://www.deedpollservice.com
Because you were married to the child�s father, he has automatically acquired parental responsibility and therefore you will need his permission for a name change to take place. If, however, the child�s birth father does not have contact or make monetary contributions to the child�s upkeep, you can apply to a court for permission to change the child�s name without the permission of the absent parent (in this case the father).