We are in a similar position as we are not married however we did mean to be before the 15 yearold was born! we also have a 14 and 6 year old. Actually the GPs probably won't bother to ask you, the receptionist will assume that it's all OK. However legally it isn't, if say their Dad took them for a vaccination and they done it, without me signing then technically it's illegal. I obviously wouldn't kick off about it. This is becoming more of a thing lately, he has managed to sign consent forms for school trips etc for years, but one in January this year was sent out with questions about who actually has Parental responsibility, so it's getting a bit harder, however you have only your son's interests at heart and even though it might not be "legal" no court in this land would disagree with your actions! The "welfare of the child is paramount" states the Children act and your actions fit perfectly. Good Luck