Valid consent for treatment / care can normally come from anyone who holds parental responsibility. The expectation is that someone with PR will be acting in the child’s best interests.
As a child grows up, the law anticipates that in time they develop the understanding and maturity to be able to make some decisions about treatment or care for themselves (this is called “Gillick” or “Fraser” competence, after a case in which a court rejected a mother’s claim that her daughters aged under 16 should not be able to access contraceptive advice and treatment without her being told).
Though still a “child” for the purposes of the Children Act 1989 until age 18, there is a presumption in law that a patient is competent to consent to their own medical treatment from age 16 (Family Law reform Act 1969, s8), though this won’t apply if the child clearly is not capable of doing so.
This means that there is a patchwork of potential decision makers. Parental responsibility continues to age 18 years, but where a parent wants treatment for a child which the child refuses, and the child is either over 16 or is younger but “Gillick competent”, it is likely that the clinicians would want to ask a Court to decide, rather than rely only on the parent’s consent.
 Parental responsibility is a set of duties, responsibilities and powers enabling specific adults to make certain significant decisions about a child. This includes decision-making in relation to a child’s living/residency arrangements, education, upbringing, medical treatment, religion etc. A Mother automatically has parental responsibility, and any other person will automatically acquire parental responsibility if married to the Mother at the time of the birth or (for births since 1.12.03) if named on the birth certificate. Parental responsibility can also be given (or removed) by a Court Order. All relevant decisions regarding a child must be discussed and agreed between all adults holding parental responsibility.
Parental responsibility gives no power for an adult’s parents to make decisions for an adult, regardless of their mental capacity. Instead, this is governed by the Mental Capacity Act 2005 (MCA).