The 5 Principles of the Mental Capacity Act 2005
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If you spend any time on placement, you’ll probably hear someone say:
“We need to check whether this patient has capacity.”
This might happen when a patient refuses treatment, wants to leave hospital or cannot seem to understand a proposed care plan.
Before anyone concludes that a person lacks capacity, there are five statutory principles that must overview the entire process. These principles come from the Mental Capacity Act 2005 and are designed to protect people without unnecessarily taking control away from them.
The starting point is not, “How do we make this decision for the patient?”
It is:
“How can we help this person make the decision themselves?”
A Quick Note About UK Law
The Mental Capacity Act 2005 applies in England and Wales.
Scotland has a separate legal framework under the Adults with Incapacity (Scotland) Act 2000. Northern Ireland also has separate legislation. Although these frameworks share values such as autonomy, participation and minimum restriction, the five principles discussed in this article are specifically those of the Mental Capacity Act.
When Should Capacity Be Assessed?
Capacity should not be assessed simply because someone is older, has dementia, behaves unusually or makes a decision that healthcare professionals disagree with.
An assessment is required when there is a genuine reason to doubt whether the person can make the particular decision. This concern might arise because of delirium, dementia, brain injury, stroke, severe mental illness, intoxication or another impairment affecting the mind or brain.
Capacity is always decision-specific and time-specific.
Someone may be able to decide what they want to eat or wear while being unable to understand a complex decision about surgery. A person may also lack capacity during an episode of delirium but regain it when the underlying illness improves.
Capacity is not a permanent label attached to the patient. It is an assessment of a particular decision at a particular time.
When there is a genuine reason to doubt capacity, the Mental Capacity Act requires a two-stage assessment.
| Stage | The question being considered | What this means in practice |
|---|---|---|
| Stage 1: Impairment or disturbance | Is there an impairment of, or disturbance in, the functioning of the person’s mind or brain? | This could include dementia, delirium, stroke, brain injury, severe mental illness, intoxication or infection affecting cognition. |
| Stage 2: Functional inability | Does that impairment or disturbance mean the person cannot make this particular decision when it needs to be made? | The assessor considers whether the person can understand, retain, use or weigh the relevant information and communicate a decision. |
The connection between the two stages matters. A person does not lack capacity simply because an impairment exists. The impairment must be causing the person’s inability to make the particular decision.
A person is unable to make the decision if, because of the impairment, they cannot understand the relevant information, retain it long enough to decide, use or weigh it as part of the process, or communicate their choice by any means.
The conclusion that someone lacks capacity must be supported by evidence and established on the balance of probabilities.
1. Always Presume Capacity
The first principle is that a person must be assumed to have capacity unless it is established that they do not.
Healthcare professionals should not assume incapacity because a patient has dementia, a learning disability, a mental health condition or difficulty communicating. Diagnosis and capacity are not the same thing.
The same applies when a patient refuses advice or makes a decision that appears risky. Disagreement is not proof of incapacity.
On placement, this means continuing to involve the patient in conversations instead of speaking only to their relatives or discussing them as though they are not present.
Bleepbook memory line:
“Start with capacity, not incapacity.”
2. Support the Person to Decide
Before concluding that someone cannot make a decision, healthcare professionals must take all practicable steps to support them.
Sometimes what looks like incapacity is actually a communication problem. The patient may need information explained more simply, extra time to process it, a professional interpreter or a communication aid. They may need their glasses, hearing aids or dentures. Pain, anxiety, tiredness and a noisy ward can also affect someone’s ability to concentrate.
Timing matters too. If the decision is not urgent, it may be appropriate to wait until the person is less distressed, more alert or recovering from a temporary condition such as delirium.
The aim is not to test whether the patient can understand complicated clinical language. The aim is to make the relevant information genuinely accessible.
Bleepbook memory line:
“Support the decision before assessing the ability.”
3. People Can Make Unwise Decisions
This principle often surprises students.
A person does not lack capacity merely because they make a decision that healthcare professionals or relatives consider unwise.
A patient with capacity may refuse medication, decline surgery, accept significant risks or choose to leave hospital despite professional advice. Healthcare staff may strongly disagree, but the patient still has the right to decide if they can understand, retain and weigh the relevant information and communicate their choice.
Capacity is about the process used to reach the decision, not whether everyone else thinks it is sensible.
An unusual decision may justify checking that the person has accurate information, is free from pressure and has received appropriate support. However, the decision itself does not prove incapacity.
Bleepbook memory line:
“A decision can be risky and still be capacitous.”
4. Act in the Person’s Best Interests
If a person genuinely lacks capacity for a particular decision, any act or decision made on their behalf must be in their best interests.
Best interests does not simply mean doing whatever appears medically safest. It requires the decision-maker to consider the person as a whole.
This includes involving the person as far as possible, considering whether they may regain capacity, examining their past and present wishes, and taking account of their beliefs, values and relationships. Relevant family members, carers and others interested in the person’s welfare may also provide important information.
However, “next of kin” does not automatically have legal authority to consent for an adult. Formal decision-making authority may come from a Health and Welfare Lasting Power of Attorney or a deputy appointed by the Court of Protection.
The team must also check whether the person has made a valid and applicable Advance Decision to Refuse Treatment. If one applies to the proposed treatment, it must be followed rather than replaced by a best-interests decision.
The goal is not to decide what everyone else wants for the patient. It is to reach a lawful, person-centred decision that reflects the individual’s rights, wishes, values and circumstances.
Bleepbook memory line:
“Best interests keeps the person, not the professionals, at the centre.”
5. Consider the Less Restrictive Option
Before acting for someone who lacks capacity, healthcare professionals must consider whether the same purpose could be achieved just as effectively in a way that restricts the person’s rights and freedom less.
This might mean providing additional support at home instead of immediately arranging residential care. It could involve reducing supervision when it is safe, using a less intrusive treatment or finding a way for the person to participate more fully.
The law does not require staff to choose an option that cannot safely or effectively achieve the required purpose. Instead, it requires them to consider whether an equally effective but less restrictive alternative exists.
Bleepbook memory line:
“Protect the person without restricting them more than necessary.”
At the time of writing in July 2026, the Deprivation of Liberty Safeguards, usually called DoLS, remain the authorisation system for adults in hospitals and care homes in England and Wales. Liberty Protection Safeguards have not replaced them.
However, the legal approach to identifying a deprivation of liberty changed following a UK Supreme Court judgment on 2 June 2026.
Older teaching often focused on a single “acid test”: whether the person was under continuous supervision and control and was not free to leave. Those factors are still relevant, but they are no longer the entire test.
The assessment must now consider the overall situation, including the type and duration of the restrictions, how they are implemented, their effect on the person, and whether the person is objecting. The person’s wishes, feelings and understanding of the arrangements also carry significant weight.
Apparent cooperation does not automatically mean valid consent. Equally, a person may sometimes be able to express valid acceptance of an arrangement even if they lack capacity to make the wider decision about their care or residence.
If there is uncertainty about whether a person is objecting, whether their acceptance is valid or whether the restrictions amount to a deprivation of liberty, staff should follow local procedures and escalate to the organisation’s Mental Capacity Act or DoLS lead. Established DoLS or court processes should continue where there is doubt.
Student nurses are not expected to make these legal determinations. Your role is to notice restrictions, listen to what the patient communicates through their words and behaviour, document factual observations and raise concerns promptly.
Capacity assessments and best-interests decisions should be clearly recorded.
The documentation should identify the exact decision being assessed, explain why capacity was questioned and describe the support given to the person. It should also show how the assessor considered the person’s ability to understand, retain, use or weigh the information and communicate a decision.
Writing only “patient lacks capacity” is not enough.
Some NHS organisations use forms called MCA1, MCA2 or similar, but these names are not nationally standardised. Always follow the documentation system used by your placement organisation.
A student nurse might document an objective observation such as:
“During discussion about the prescribed antibiotic, the patient was unable to explain its purpose or describe the possible consequences of refusing it, despite the information being repeated in plain language. Registered nurse informed.”
This records what happened without the student independently making a formal legal conclusion.
Students will not usually lead complex capacity assessments, but their observations can make a real difference.
You may notice that a patient becomes more confused later in the day, understands information when pictures are used or communicates more effectively when their hearing aids are fitted. You may also be the first person to notice that someone is repeatedly trying to leave, appears frightened by restrictions or is agreeing without seeming to understand what is happening.
Report these observations to your supervisor or the relevant registered professional. Capacity assessment is a team responsibility in practice, even though the person responsible for the particular decision remains the legal decision-maker.
The Mental Capacity Act is not designed to take decisions away from people.
Its starting point is that people should remain in control of their own lives wherever possible. Healthcare professionals must presume capacity, provide meaningful support and respect a person’s right to make choices others may consider unwise.
Only when a person genuinely cannot make the particular decision should somebody act on their behalf and even then, the person’s wishes, values, freedom and rights must remain central.
Bleepbook memory line:
“Presume. Support. Respect. Protect. Restrict less.”
Mental Capacity Act 2005: Code of Practice
NICE NG108: Decision-making and mental capacity
Deprivation of Liberty Code of Practice
Department of Health and Social Care: UK Supreme Court 2026 judgment on deprivation of liberty
Scottish Government: Adults with Incapacity, communication and assessing capacity