Child is 3 but unaware of surname. His dad is not in contact, likely never will be and is not named on the birth certificate. At the time of registering his birth I gave him ex's surname. I'd like to change this to my surname before he starts school. Do I need to apply for a new birth certificate or go through deed pool? If deed pool does this over ride the birth certificate so he will have my surname once his national insurance card arrives? I've googled and I've found it very confusing.