What are the five principles of the Mental Capacity Act 2005?
Section 1 of the Mental Capacity Act 2005 sets out five principles that apply to every act and decision made under it. The Act covers people aged 16 and over in England and Wales. Scotland has the Adults with Incapacity (Scotland) Act 2000 and Northern Ireland has the Mental Capacity Act (Northern Ireland) 2016, so check the law where you work.
| Principle | What it means | Example |
|---|---|---|
| 1. Presume capacity | Assume a person has capacity unless it is shown that they lack it | A diagnosis of dementia or learning disability does not on its own mean someone cannot decide |
| 2. Support decision-making | A person is not treated as unable to decide until all practicable steps to help them have failed | Using pictures, an interpreter or choosing the time of day they are most alert |
| 3. Unwise decisions | Making an unwise decision does not mean a person lacks capacity | A man with capacity refuses a recommended operation because he values staying at home |
| 4. Best interests | Anything done for a person who lacks capacity must be in their best interests | Choosing treatment that fits what the person valued, not just what is clinically neat |
| 5. Less restrictive option | Consider whether the aim can be achieved in a way that restricts the person's rights and freedom less | Using a bed sensor instead of bed rails, or supervision instead of locking a door |
What makes consent valid?
Valid consent has three elements. The person must have capacity for the decision, must have enough information presented in a way they can understand, and must decide voluntarily, free from pressure by staff, family or anyone else. A signed form is evidence that a discussion happened. It is not consent in itself.
| Element | Common failure |
|---|---|
| Capacity | Assuming a person with dementia cannot consent to anything |
| Information | Not mentioning a less invasive option because the clinician prefers surgery |
| Voluntariness | A relative pressuring an older person, or staff implying care will stop if they refuse |
What did Montgomery change?
In Montgomery v Lanarkshire Health Board (2015), the UK Supreme Court held that clinicians must take reasonable care to make sure patients know about any material risks of recommended treatment and about reasonable alternatives. A risk is material if a reasonable person in the patient's position would be likely to think it significant, or if the clinician knows or should know that this particular patient would. The GMC's guidance Decision making and consent (2020) describes this as a dialogue: find out what matters to the person, share relevant information and support them to decide.
Two people are offered the same hand operation, which carries a small risk of reduced fine finger movement. For one, a retired office worker, this is a minor concern. For the other, a professional violinist, it could end her career. Under Montgomery, the clinician must find out what matters to each person and discuss the risks that are material to them.
- Ask what the person already knows and what matters most to them.
- Explain the options, including doing nothing, with benefits and risks in plain language.
- Include serious risks even if rare, and common risks even if minor.
- Use a professional interpreter rather than family, especially not children.
- Check understanding, for example by asking the person to explain the plan back.
- Record the specific risks and alternatives discussed, not only that a form was signed.
How do you assess mental capacity?
Under sections 2 and 3 of the Act, a person lacks capacity for a matter if they cannot make the decision because of an impairment of, or disturbance in the functioning of, the mind or brain. The Supreme Court has confirmed that the assessor should first ask whether the person can make the decision and then whether any inability is caused by an impairment or disturbance. The person proposing the treatment or care usually assesses capacity for that decision.
- Understand: Can the person understand the information relevant to the decision, including the likely consequences of each choice or of not deciding?
- Retain: Can they hold on to the information long enough to make the decision? Retaining it only briefly is enough.
- Use or weigh: Can they use or weigh the information to reach a decision? This is often where capacity is lost, for example when someone can repeat the risks but cannot apply them to themselves.
- Communicate: Can they communicate their decision by any means, including speech, writing, sign language, gestures or blinking?
- Link to an impairment: If they cannot do one or more of these, is that because of an impairment or disturbance of the mind or brain, such as dementia, delirium, brain injury or intoxication? It may be temporary or permanent.
Patient confused. Lacks capacity. Proceed in best interests.
Decision: whether to have surgery for a fractured right hip. Explained in simple terms at 10:00 when most alert, hearing aid in, daughter present. Mr H said surgery would 'fix my leg' but twice said that without it he would be walking in a couple of days. He could not understand or weigh the consequences of refusing. This is caused by his known vascular dementia; no signs of delirium today. Conclusion: lacks capacity for this decision now; unlikely to regain it in the time available. Best interests process to follow.
What are all practicable steps to support a decision?
The second principle is often skipped under time pressure, yet it is where many capacity concerns arise. Before concluding someone cannot decide, ask what you could do to help them.
- Choose a quiet place and the time of day when the person is most alert.
- Use simple language, pictures, easy-read leaflets or objects.
- Make sure hearing aids, glasses and dentures are in, and use a professional interpreter if needed.
- Involve someone the person trusts, or a speech and language therapist, to help communication.
- If the decision can wait, treat reversible causes of confusion such as infection, pain or medication side effects first.
How are best interests decisions made?
Section 4 of the Act sets out what the decision-maker must consider. Best interests is not the same as what the clinician thinks is medically best. It is about what is right for this person, taking into account their wishes, beliefs and values.
- Do not make assumptions based on age, appearance, condition or behaviour.
- Consider whether the person may regain capacity and whether the decision can wait.
- Involve the person as fully as possible.
- Consider their past and present wishes and feelings, beliefs and values, including anything written down.
- Consult family, carers, anyone the person named, and any attorney or deputy, where practicable.
- For life-sustaining treatment, do not be motivated by a wish to bring about the person's death.
| Who or what | What it means |
|---|---|
| Lasting Power of Attorney (health and welfare) | A registered attorney can decide within the scope of the LPA. They can refuse life-sustaining treatment only if the LPA expressly allows it. Check the registered document. |
| Court-appointed deputy | Appointed by the Court of Protection; cannot refuse life-sustaining treatment for the person |
| Advance decision to refuse treatment | If valid and applicable, it has the same effect as a refusal made at the time. For life-sustaining treatment it must meet extra formal requirements, including being written, signed and witnessed |
| Independent Mental Capacity Advocate | Must be instructed for serious medical treatment or certain accommodation moves when there is no one appropriate to consult other than paid carers, except in an emergency |
What about emergencies, restraint and deprivation of liberty?
In an emergency where a person lacks capacity and there is no time to consult, you may give treatment that is immediately necessary in their best interests. Section 5 protects you from liability when you reasonably believe the person lacks capacity and the act is in their best interests. Restraint is only allowed under section 6 if it is necessary to prevent harm to the person and proportionate to the likelihood and seriousness of that harm.
If care for a person who lacks capacity amounts to a deprivation of liberty, for example continuous supervision and control without freedom to leave, it needs lawful authorisation. In hospitals and care homes in England and Wales this is currently through the Deprivation of Liberty Safeguards. The government has been consulting again on replacing them with the Liberty Protection Safeguards, so check your organisation's current policy and speak to your MCA or safeguarding lead.
How is consent different for children and young people?
| Age | Who can consent | Key point |
|---|---|---|
| Under 16 | The child if Gillick competent for the decision; otherwise someone with parental responsibility | Gillick competence is decision-specific: does the child understand what is proposed well enough? |
| 16 and 17 | The young person is presumed to have capacity to consent | The MCA applies to most decisions. Refusals of treatment are legally complex, so seek senior and legal advice |
| 18 and over | The adult, or the MCA framework if they lack capacity | Parents have no authority to consent for an adult child |
If a concern has been raised about consent or capacity
Consent and capacity concerns often come from a patient who says a risk was never mentioned, from treatment given against someone's wishes without a proper assessment, or from someone who clearly lacked capacity being left without care because staff thought they could not act. Good reflection names which principle or step was missed, why, and what you now do and record differently. If a complaint, claim or regulator referral is involved, get advice from your defence organisation or union first. This guide is educational, not legal advice.
Our course Consent and Mental Capacity Act Training works through valid consent and Montgomery, the five principles, capacity assessment, best interests and the rules for children, with worked examples and a guided reflection. The courses on medication errors and record keeping are related options if your learning plan is broader.
Frequently asked questions
What are the 5 principles of the Mental Capacity Act in simple terms?
Assume the person can decide unless shown otherwise. Help them decide before concluding they cannot. Do not treat an unwise choice as a lack of capacity. If they cannot decide, act in their best interests. And choose the option that restricts their rights and freedom least.
What is the two-stage test of capacity?
Traditionally it asks whether there is an impairment or disturbance of the mind or brain, and whether it makes the person unable to decide. The Supreme Court has said the functional question comes first: can the person understand, retain, use or weigh the information and communicate a decision? Then ask whether any inability is caused by an impairment.
Can a family member consent on behalf of an adult patient?
Not in England and Wales, unless they hold a registered health and welfare Lasting Power of Attorney covering the decision or have been appointed as a deputy by the Court of Protection. Family members should be consulted about the person's wishes and best interests, but they cannot give or refuse consent simply as next of kin.
Who should assess mental capacity?
Usually the person proposing the treatment, care or action assesses capacity for that specific decision. For example, the clinician recommending surgery assesses capacity to consent to that operation. For complex cases, seek support from senior colleagues, specialists or your MCA lead and record the assessment clearly.
Does a patient with dementia lack capacity?
Not automatically. A diagnosis alone never establishes a lack of capacity. Many people with dementia can make many of their own decisions, especially with support. Capacity must be assessed for each decision at the time it needs to be made, after all practicable steps to help the person have been taken.
What does material risk mean in consent?
Following Montgomery, a risk is material if a reasonable person in the patient's position would be likely to attach significance to it, or if the clinician knows or should know that this particular patient would. Clinicians must also discuss reasonable alternatives, including doing nothing.
Does the Mental Capacity Act apply to 16 year olds?
Yes. The Mental Capacity Act 2005 applies to people aged 16 and over in England and Wales, and 16 and 17 year olds are presumed to have capacity to consent to treatment. Refusals of treatment by under-18s are legally complex, so seek senior and legal advice in those situations.
Related courses
Consent and Mental Capacity Act Training
This course explains what makes consent valid in UK law and professional guidance, including the Montgomery judgment, and how to apply the Mental…
Medication Errors: Reflection and Remediation
This course explains why medication errors happen, what you must do when one occurs, and how to show a regulator or employer that you have understood…
Record Keeping and Documentation: Remediation Course
This course explains what good clinical documentation looks like, why record-keeping concerns arise, and why altering or falsifying a record is…
Sources and further reading
- Mental Capacity Act 2005. legislation.gov.uk.
- Mental Capacity Act 2005 Code of Practice. Office of the Public Guardian.
- Decision making and consent. General Medical Council.
- Montgomery v Lanarkshire Health Board [2015] UKSC 11. UK Supreme Court.
- The Code: Professional standards of practice and behaviour for nurses, midwives and nursing associates. Nursing and Midwifery Council.
- Standards of conduct, performance and ethics. Health and Care Professions Council.
Practitioner Insight is an independent education provider. It is not affiliated with or endorsed by the GMC, MPTS, NMC, HCPC, GPhC or any NHS organisation, and this information is not legal advice. If you have been referred to a regulator, speak to your defence organisation, trade union or legal representative.
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