What makes consent valid
Consent is not a form and it is not a signature. In law it is a decision made by a particular person, about a particular intervention, at a particular time. Three things must be true at once for it to count.
- The person has capacity to make this decision.
- The decision is voluntary — free of coercion or undue influence from clinicians, family, partners or anyone else.
- The person is adequately informed: what is proposed, why, what it involves, what could follow, and what else could be done instead.
Remove any one and the consent fails, however neatly the paperwork was completed. A patient who signs on a trolley outside theatre, having never discussed the alternatives, has signed something; they have not consented. Most consent in medicine is verbal and entirely valid, and it can be withdrawn at any point.
- Material risk
- A risk a reasonable person in this patient’s position would attach significance to, or that this patient in particular would.
- Best interests
- The standard used when an adult lacks capacity. Wider than best medical interests: it takes in wishes, beliefs and values.
- Gillick competence
- Sufficient understanding and intelligence for a child under 16 to consent to a specific proposed treatment.
- Advance decision
- A refusal of specified treatment made ahead of time by an adult with capacity. Binding if valid and applicable.
Montgomery and the move to the reasonable patient
For decades, how much a doctor had to disclose was judged by the professional standard: would a responsible body of doctors have mentioned this risk? That left the scope of disclosure in the profession’s own hands.
Montgomery v Lanarkshire Health Board (2015) ended that for consent. Nadine Montgomery was a woman of small stature with diabetes, whose baby faced a substantially raised risk of shoulder dystocia in vaginal delivery. She was not told of that risk and was not offered elective caesarean as an alternative; her son was born with severe disability. The Supreme Court held the test is no longer what a reasonable doctor would say. The case came from Scotland and the principle applies UK-wide.
The duty is to take reasonable care to ensure the patient is aware of any material risks in the proposed treatment and of any reasonable alternatives, including doing nothing. Materiality is judged from the patient’s side: would a reasonable person in this position attach significance to the risk, or should the doctor know that this patient would? A small risk to the voice is immaterial to most people and enormous to a singer.
Montgomery changed the activity, not just the threshold
You cannot match risks to a person you have not asked about, which is why the case turns consent into a conversation rather than a recitation. Find out what this patient is trying to protect, then tell them what someone who cares about that would want to know.
The narrow therapeutic exception survives — information may be withheld where disclosure would be seriously harmful to the patient’s health — but it is not a licence to withhold something because it might change their mind.
The Mental Capacity Act 2005: five principles, two stages
In England and Wales, capacity is governed by the Mental Capacity Act 2005, which applies from age 16 for most purposes. Five statutory principles sit at the front of the Act, and interviewers expect you to be able to give them.
- Assume capacity unless it is established that the person lacks it.
- Do not treat someone as unable to decide until all practicable steps to help them decide have been tried without success.
- An unwise decision is not, by itself, evidence of incapacity.
- Anything done for a person who lacks capacity must be in their best interests.
- Before acting, consider whether the purpose can be achieved in a way less restrictive of their rights and freedom.
Principles two and three carry most of the weight. Support to decide means an interpreter, a quieter room, the time of day when the person is sharpest, treating the urinary tract infection first. Capacity is often something you build rather than something you discover.
The test itself has two stages and both must be met. First, is there an impairment of, or a disturbance in the functioning of, the mind or brain, permanent or temporary? Dementia, delirium, psychosis, learning disability, intoxication and brain injury can all satisfy that first limb, though none of them settles the second. Second, and because of that impairment, is the person unable to do any one of four things?
- Understand the information relevant to this decision.
- Retain it long enough to make the decision — briefly is enough.
- Use or weigh that information as part of deciding.
- Communicate the decision, by any means at all.
Two qualifiers do a lot of work. Capacity is decision-specific: the same man may lack capacity to weigh cardiac surgery while retaining capacity to decide what he eats. It is time-specific too, fluctuating with delirium, sedation and infection, so a decision that can safely wait should wait for a lucid interval. Capacity is never inferred from age, appearance or diagnosis.
The circular capacity assessment
The commonest failure is to reason backwards from the answer: the patient refused, the refusal looks irrational, therefore she must lack capacity. The Act blocks this explicitly. Incapacity is shown by how a person reasons, never by the conclusion they reach. If capacity is only questioned when patients disagree with the team, that is not an assessment.
A 78-year-old man with moderate dementia refuses an operation to fix a fractured hip. The surgical team think he needs it. What do you do?
Do not start with the dementia; a diagnosis is not an answer to a capacity question. Ask whether he can make this decision now: can he understand what the fracture and the operation mean, hold that in mind, weigh it against not operating, and tell you? Optimise first — treat delirium and pain, bring in someone he trusts, try again when he is at his best. If he has capacity, his refusal stands even if it shortens his life. If not, the question becomes best interests in the round: what he said when he was well, what the people who know him say, and the least restrictive route to being comfortable and mobile.
When capacity is absent: best interests, and who speaks for the patient
Being next of kin confers no power to consent for an adult, and "so we ask the family to consent" is a real legal error. The only people who can consent on an adult’s behalf in England and Wales are an attorney under a registered health and welfare lasting power of attorney, a deputy appointed with that authority, or the Court of Protection itself. Where none of those exists — which is most of the time — nobody signs for the patient: the clinician proposing the treatment decides in the patient’s best interests. What relatives do is inform that decision, which is often the only route to what the person valued.
Best interests is deliberately broad. The decision-maker must consider whether capacity is likely to return and whether the decision can wait, involve the person as far as possible, and take account of their past and present wishes, beliefs and values. Carers, family and anyone holding formal authority must be consulted. It is the patient’s interests seen from the patient’s point of view.
Three instruments matter here, and interviewers ask for them by name.
- Advance decision to refuse treatment: made in advance by an adult with capacity. If valid and applicable to the situation that has arisen, it binds exactly as a contemporaneous refusal would. Where it covers life-sustaining treatment it must be written, signed and witnessed, and must state that it applies even if life is at risk. Advance requests for treatment are not binding.
- Lasting power of attorney for health and welfare: an attorney appointed while the person still had capacity, registered with the Office of the Public Guardian. It takes effect only once capacity is lost, and covers life-sustaining treatment only if the document says so expressly.
- Independent Mental Capacity Advocate (IMCA): instructed when someone lacking capacity faces serious medical treatment or a long-term move of accommodation and has no appropriate family or friend to consult. The IMCA represents the person but does not decide.
Where a decision is finely balanced, genuinely disputed, or reserved by law to a judge, the Court of Protection decides. Seeking a declaration is good practice, not failure.
A woman who is a Jehovah’s Witness is bleeding heavily after surgery and refuses a blood transfusion. She will probably die without one.
Start from the presumption that she has capacity. If she does, the refusal is determinative: a competent adult may refuse life-saving treatment for reasons others find wrong, or for no reason at all, and transfusing her anyway would be an unlawful battery. Then test the other two limbs. Is it voluntary — has anyone been applying pressure, and would she say the same alone? Is it informed — does she understand this refusal may kill her, and what is offered instead? The strongest answers move on to the work that respecting autonomy demands: cell salvage, tranexamic acid, meticulous haemostasis, iron and erythropoietin, early contact with the local hospital liaison committee, and establishing which specific products or fractions she accepts, because that varies between individuals.
Children and young people, including the part the law has not settled
Age draws three lines. From 18, the adult rules apply. At 16 and 17, a young person in England and Wales is presumed able to consent to their own treatment under the Family Law Reform Act 1969, and a parent does not need to consent as well — though involving parents is usually good practice.
Under 16 there is no presumption either way. A child may consent if they are Gillick competent, from the 1985 House of Lords decision: sufficient understanding and intelligence to understand fully what is proposed. Competence is assessed for the specific decision — a twelve-year-old may be competent to consent to a vaccination and not to major surgery.
Where a child is not competent, someone with parental responsibility consents for them, and that consent is itself constrained by the child’s best interests. Consent from one holder is normally sufficient, though a small category of decisions needs agreement or a court.
The messy part is refusal. In a 1992 Court of Appeal case, Re W, a 16-year-old with anorexia nervosa refused treatment, and the court held her refusal could be overridden: consent from someone with parental responsibility, or from the court, could authorise treatment anyway. That left an asymmetry that still troubles the law — a competent young person’s yes is decisive, their no may not be.
Should a competent young person’s refusal be overridable?
Why the courts have allowed it
- The consequences are asymmetric: agreeing to treatment risks little, refusing life-saving treatment risks everything, so a higher bar for refusal can be argued as proportionate.
- Conditions that often produce refusal in adolescence, anorexia nervosa among them, can impair the very reasoning the competence test is measuring.
- It has been framed as preserving a young person’s open future, so they reach adulthood still able to decide.
- In practice the jurisdiction is invoked rarely, and typically where death or severe permanent harm is in prospect.
Why it is criticised
- It is logically incoherent: the same understanding is deemed sufficient to accept treatment and insufficient to decline it.
- An autonomy that operates only when the patient agrees with the clinician is not really autonomy.
- Overriding a sustained, competent refusal causes its own serious harm, including to the young person’s trust in doctors.
- Critics argue it sits awkwardly with human rights law and with the logic of Gillick, and point out that the Supreme Court has never revisited the question.
Treat this as contested rather than settled. Where refusal could lead to death or severe permanent injury, the expected step is to seek legal advice quickly rather than act unilaterally in either direction.
A 15-year-old asks you for contraception and does not want her parents to know.
Open with what you would not do: refuse on age alone, or tell her parents reflexively. Assess whether she is Gillick competent, then work through the Fraser criteria — that she understands the advice, that you have encouraged her to involve a parent and she will not be persuaded, that she is likely to have sex with or without contraception, that her health is likely to suffer without it, and that her best interests support providing it. Then show the safeguarding instinct, because that is what the station is really testing: who the partner is and how old he is, and whether there is any sign of coercion or exploitation. Confidentiality here is strong but not absolute, and when it gives way is a separate question.
The other UK jurisdictions, and how to use this in the room
The Mental Capacity Act 2005 covers England and Wales only. Scotland uses the Adults with Incapacity (Scotland) Act 2000, which applies from 16 and runs on its own principles: benefit to the adult, the minimum necessary intervention, regard for the adult’s past and present wishes, consultation with relevant others, and encouragement of whatever skills the adult retains. Treatment is generally authorised by a certificate of incapacity, and Scotland has welfare attorneys and guardians. Northern Ireland has its own Mental Capacity Act (Northern Ireland) 2016, which has been commenced in stages and, at the time of writing, is not yet fully in force.
Deployment matters as much as content. Consent and capacity rarely arrive as a knowledge question; they arrive inside a scenario, and the marks are for the reasoning you show. Anchor the answer in autonomy without letting autonomy swallow everything — the four pillars still have to be balanced — and use the structure in answering a dilemma live so you do not commit in your first sentence.
And if a station asks you to take consent from an actor rather than discuss it, the marks live in the dialogue: what she already understands, what she is worried about, the material risks in her terms, the alternatives including no treatment, and a genuine invitation to ask. Longer worked scenarios sit in the ethics guide.