Mental Capacity Assessments
The Mental Capacity Act 2005
The statutory framework governing every lawful capacity assessment in England and Wales
What is the Mental Capacity Act 2005?
The Mental Capacity Act 2005 is the statute governing how decision-making capacity is assessed, and how decisions are made for people who cannot make them for themselves. It applies across England and Wales, and every lawful capacity assessment must follow the statutory structure it sets out. Applying the framework incorrectly can invalidate decisions, undermine court proceedings and result in expert reports being rejected.
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England and Wales
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When concerns arise about whether a person can make a specific decision, this is the statute that governs the assessment. The Act is decision-specific by design: it does not ask whether someone has capacity in general, but whether they can make this decision at this time.
This guide explains how the Act operates in practice, how the legal test is applied and where capacity assessments commonly fail.
What the Act provides the legal foundation for
The Act underpins a wide range of legal and practical situations, including:
- Decision-specific mental capacity assessments
- Best interests decision-making
- Deputyship applications and COP3 assessments
- Capacity to grant a Lasting Power of Attorney
- Litigation capacity under CPR Part 21, with expert evidence under CPR Part 35
- Testamentary capacity, where the common law test in Banks v Goodfellow also applies
- Capacity to manage finances, residence decisions and trustee capacity
- Retrospective capacity assessments and disputes
- Protection of vulnerable adults
The five statutory principles
At the heart of the Act sit five mandatory principles. They are not guidance, they are law, and every assessment and decision must demonstrate compliance with them:
- Presumption of capacity. Every adult is presumed to have capacity unless it is established otherwise. Capacity is not removed because a person has a diagnosis, appears vulnerable, makes an unwise decision or disagrees with professionals.
- Support to make a decision. A person must be given all practicable help before being treated as unable to decide, including simplified explanations, visual aids, adjusted timing, communication support and the use of interpreters or advocates.
- The right to make unwise decisions. A decision others consider imprudent does not equal incapacity. The Act protects autonomy, including risky or unconventional choices.
- Best interests. If a person lacks capacity for a specific decision, any act done or decision made on their behalf must be made in their best interests, following a structured statutory process.
- The least restrictive option. Any intervention must restrict the person's rights and freedom of action as little as possible.
Where capacity assessments go wrong
- Confusing a diagnosis with incapacity
- Failing to identify the specific decision being assessed
- Skipping the causative nexus analysis
- Inadequate exploration of the use or weigh element
- Over-reliance on risk as evidence of incapacity
- Insufficient evidence gathering
- Confusing a diagnosis with incapacity
- Failing to identify the specific decision being assessed
- Skipping the causative nexus analysis
- Inadequate exploration of the use or weigh element
- Over-reliance on risk as evidence of incapacity
- Insufficient evidence gathering
The two-stage legal test
Capacity is always decision-specific and time-specific. A person may have capacity for one decision but not another, and capacity may fluctuate. The legal test is structured in two stages, applied functional test first.
Stage one, the functional test. Can the person make this specific decision? A person is unable to make a decision if they cannot understand the relevant information, retain it long enough to decide, use or weigh it as part of the decision-making process, or communicate their decision by any means. Each element must be considered separately.
Stage two, the causative test. Is that inability because of an impairment of, or a disturbance in, the functioning of the mind or brain? Examples include dementia, delirium, brain injury, learning disability, severe mental illness and intoxication. Both stages must be satisfied. It is not enough to identify a diagnosis, and it is not enough to show risk.
The causative nexus. This is one of the most misunderstood aspects of the Act. To conclude lawfully that a person lacks capacity, an assessment must show what the impairment is, what the functional difficulty is, and how the impairment causes that difficulty. Without that link there is a real risk of confusing risk-taking behaviour, family disagreement, professional frustration or vulnerability with legal incapacity. Diagnosis does not equal incapacity, disagreement does not equal incapacity, and risk does not equal incapacity. The causative nexus is often where reports succeed or fail under scrutiny.
Capacity evidence prepared by specialist professionals
Nellie Supports is a social work led multidisciplinary specialist practice working across England and Wales, operating through a permanent, full-time employed team that has completed more than 11,000 assessments. Our mental capacity work spans decision-specific assessments, COP3 reports, testamentary and litigation capacity, retrospective assessments and critical reviews of existing reports, all built on the statutory framework this guide describes.
Frequently Asked Questions
Is the Mental Capacity Act 2005 means-tested?
No. The Act governs decision-making capacity, not funding.
Does a diagnosis automatically mean someone lacks capacity?
No. A diagnosis alone is insufficient. The functional test must be applied, and the impairment must be shown to cause the inability to decide.
Can capacity fluctuate?
Yes. Capacity can vary with time, health and the complexity of the decision, which is why assessments are decision-specific and time-specific.
Who can carry out a mental capacity assessment?
Any suitably trained professional may assess capacity, but court proceedings often require experienced assessors and reports compliant with CPR Part 35.
Is testamentary capacity governed by the MCA?
Not directly. Testamentary capacity follows the Banks v Goodfellow test, though MCA principles often inform modern practice.
This guide is general information about the Mental Capacity Act 2005 in England and Wales, not legal advice, and does not create a professional relationship. Nellie Supports provides independent social work assessment, evidence and advocacy support. We do not provide regulated legal advice, and where a legal remedy is needed we will say so and support your solicitor's work.