E & F (Minors : Blood Transfusion)  EWCA Civ 1888 (on Bailii).
The above recent decision of the England and Wales Court of Appeal appears consistent with recent Australian decisions. The reasons opened with the following:
These are appeals brought by two young persons from orders made by judges of the Family Division in which it was declared under the inherent jurisdiction that, although the young persons were competent to decide whether to consent to or refuse medical treatment in the form of blood transfusion, it would nevertheless be lawful for their doctors to administer blood to them in the course of an operation if that became necessary to prevent serious injury or death.
The appellants are E, a girl who was aged 16 years 8 months at the time of the decision under appeal, and F, a boy who was aged 17 years 5 months at the time of the decision in his case. Each of them has been baptised as one of Jehovah’s Witnesses and conscientiously rejects blood transfusions as an article of faith. Each was considered by their doctors to have the capacity to make decisions about their medical treatment, i.e. to be Gillick competent (see Gillick v West Norfolk and Wisbech Area Health Authority and Another  AC 112). They had made their decisions independently and had the support of their parents.
Some decisions about medical treatment have to be made in the certain knowledge that a medical crisis has arisen. That was not the position here. The declarations were made in relation to the treatment that could be given if a crisis arose. That was statistically unlikely to happen, but if it did, the consequences were potentially very serious. Happily, no crisis arose in either case, transfusion did not occur, and both young persons were soon safely discharged from hospital.
In that sense, the declarations never formally came into effect. E and F are nevertheless aggrieved that their autonomy was overruled, and distressed by the process that occurred. In their applications for permission to appeal they advanced two main arguments. The first was that the State, acting through the court, has no power to overrule the capacitous decision of a mature minor, and in particular a young person aged 16 or 17. The second was that any such power was wrongly exercised in their cases. Permission to appeal was refused in relation to the first argument because it is settled law that the court has the power to intervene in the best interests of a minor even if the effect is to overrule a decision that would be conclusive if the young person had made it after reaching the age of 18. The real question, with which this judgment is concerned, is not whether the power exists, but how it should be exercised.
At  the Court stated that when the court is being asked to exercise its inherent jurisdiction, there are three stages. The first is to establish the facts. The second is to decide whether it is necessary to intervene. If it is, the final and decisive stage is the welfare assessment.
Welfare assessments in medical treatment cases concerning young persons with decision-making capacity involve the balancing of two transcendent factors: the preservation of life and personal autonomy. . The Court concluded at :
Finally, on the issue of principle, we do not accept the argument, based on An NHS Trust v A and AC v Manitoba, that there is a point where the decision of a capacitous young person becomes “determinative” and where respecting such a decision is “by definition in his or her best interests”. Again, care needs to be taken with the word ‘determinative’. Insofar as it is said to mean that the young person is the ultimate decision-maker, that is not so. Their decision may be the determinative factor in the court’s welfare evaluation, but that is in the different sense that it is the factor that has been found to predominate.