Gillick ruling (1985) was primarily about sharing of information with parents (use of oral contraceptive), not about going against their decision!

You should involve children and young people as much as possible in decisions about their care, even when they are not able to make decisions on their own (GMC).

Competence is not binary, it varies according to context and over time.  You need to assess ability to:

• understand, retain, use and weigh Information about consequences of treatment/non-treatment
• Communicate

And you need to assess context:

• Complexity, level or risk, seriousness of consequences
• Physical/emotional development
• Changes in health/treatment

Even then, you should encourage involvement of parents.  In difficult situations, consider involving multidiscip team, independent advocate, child protection teams. ”You should not make unjustified assumptions about a child or young person’s best interests based on irrelevant or discriminatory factors, such as their behaviour, appearance or disability”.

At 16yrs, a young person can be presumed to have the capacity to consent.  In Scotland, parents cannot authorize treatment a competent young person (even under 16yr) has refused.  In E&W/NI, High Court can override up to 18yrs – “children and young people have a right to consent, but not to refuse treatment if this would put their health in serious jeopardy” (BMA consent toolkit).  Court rulings have gone both ways.