This chapter provides information for multi-agency practitioners in relation to working with adults who lack mental capacity. It outlines the principles of the Mental Capacity Act, to which all practitioners should adhere in their work. It outlines the two stage test for assessing capacity, and some of the safeguards which exist to safeguard adults who lack capacity.


Best Interests

Consent in Safeguarding Enquiries 

Deprivation of Liberty Safeguards


Mental Capacity Act 2005 Code of Practice (Office of the Public Guardian)

Mental Capacity Act, SCIE

Decision-Making and Mental Capacity (NICE) 

Carrying Out and Recording Capacity Assessments (39 Essex Chambers)

Fluctuating Capacity in Context (39 Essex Chambers)

Mental Capacity Toolkit (University of Bournemouth) 

Mental Capacity Act (MCA): e-Learning course (SCIE)

February 2024: A new section 4,3, Causative nexus has been added.

1. Definition

The Mental Capacity Act 2005 (MCA 2005) provides a framework to protect and restore power to those who may lack, or have reduced, mental capacity to make certain decisions at particular times. It places the adult at the centre of the decision making process.

Whenever the term ‘a person who lacks capacity’ is used, it means a person who lacks capacity to make a particular decision or take a particular action for themselves at the time the decision or action needs to be taken.

This reflects the fact that people may lack capacity to make some decisions for themselves but will have capacity to make other decisions. For example, they may have capacity to make small decisions about everyday issues such as what to wear or what to eat but lack capacity to make more complex decisions about financial matters.

It also reflects the fact that a person who lacks capacity to make a decision for themselves at a certain time may be able to make that decision at a later date. This may be because they have an illness or condition that means their capacity changes. Alternatively, it may be because at the time the decision needs to be made, they are unconscious or barely conscious whether due to an accident or being under anaesthetic or their ability to make a decision may be affected by the influence of alcohol or drugs.

Finally, it reflects the fact that while some people may always lack capacity to make some types of decisions – for example, due to a condition or severe learning disability that has affected them from birth – others may learn new skills that enable them to gain capacity and make decisions for themselves’ (MCA 2005 Code of Practice: p3).

The MCA legislates in relation to:

  • allowing adults to make as many decisions as they can for themselves;
  • enabling adults to make advance decisions about whether they would like future medical treatment;
  • allowing adults to appoint, in advance of losing mental capacity, another person to make decisions about personal welfare or property on their behalf at a future date;
  • allowing decisions concerning personal welfare or property and affairs to be made in the best interests of adults when they have not made any future plans and cannot make a decision at the time;
  • ensuring an NHS body or local authority will appoint an independent mental capacity advocate to support someone who cannot make a decision about serious medical treatment, or about hospital, care home or residential accommodation, when there are no family or friends to be consulted;
  • providing protection against legal liability for carers who have honestly and reasonably sought to act in the person’s best interests;
  • providing clarity and safeguards around research in relation to those who lack capacity.

The MCA relates to people over the age of 16 years old. However, these policies and procedures only apply to adults, over the age of 18 years old.

2. Principles of the Mental Capacity Act

The following five principles apply for the purposes of the MCA:

  • it must be assumed that a person has mental capacity unless they have been assessed as lacking mental capacity;
  • a person should not be treated as unable to make a decision unless all practicable steps to help them do so have been taken without success;
  • a person should not be treated as unable to make a decision just because they make a decision that seems to others to be unwise or wrong;
  • an act or decision carried out for the person who lacks mental capacity must be done in their best interests;
  • before an act or decision is carried out, there must be consideration given to achieving the intended outcome in a way that is less restrictive of the person’s rights and freedoms.

These five principles should inform all actions when working with a person who may lack or have reduced mental capacity and should be evidenced when making decisions or agreeing actions on their behalf.

3. Determining Capacity

As noted in Section 2, it must be assumed that an adult has the mental capacity to make their own decisions unless it is established that they lack the capacity to do so. This means that anybody who claims an adult lacks mental capacity should be able to provide evidence in support of this.

They need to demonstrate, on the balance of probabilities, that the adult lacks the mental capacity to make a particular decision, at the time it needs to be made. This means being able to demonstrate it is more likely than not that the person lacks capacity to make the decision in question

3.1 Two Stage Test

To help decide if a person lacks capacity, the MCA sets out a two stage test.

Stage 1: The Functioning Test – can the adult make the decision in question?

This involves looking at whether the adult is able to make the required decision.

Practical and appropriate support should be provided to help the adult make the decision for themselves, if required.

An adult is considered unable to make a decision if they cannot:

  1. understand information about the decision to be made (known as the ‘relevant information’);
  2. keep that information in their mind;
  3. use or weigh up that information as part of the decision making process; or
  4. communicate their decision (by talking, using sign language or any other means).

There only needs to be evidence in one of these areas, not all of them.

If the adult cannot make the decision in question – even with support – Stage 2 must then be considered.

Stage 2: The Diagnostic Test – is the person unable to make the decision because of an impairment or disturbance in the functioning of their mind or brain?

This requires evidence to show the person has an impairment or disturbance of the mind or brain. Examples include:

  • conditions associated with some forms of mental illness;
  • dementia;
  • significant learning disabilities;
  • the long term effects of brain damage;
  • physical or medical conditions that cause confusion, drowsiness or loss of consciousness;
  • delirium;
  • concussion following a head injury; and
  • effects of alcohol or drug use.

If a person does not have such an impairment or disturbance of the mind or brain, they will not lack mental capacity under the MCA.

Once the adult has been identified as having an impairment or disturbance in the functioning of the mind or brain, it is important to determine that their inability to make the decision is because of this impairment. This is known as the ‘causative nexus’ (PC and NC v City of York Council [2013] EWCA Civ 478). Only where it can be reasonably said that the person cannot make the decision because of the impairment of their mind, can it be said that they lack mental capacity to make the decision.

Assessors should also consider the case of SS v London Borough of Richmond upon Thames and South West London Clinical Commissioning Group [2021] in which Mr Justice Hayden, Vice President of the Court of Protection highlighted (SS v London Borough of Richmond Upon Thames & Anor [2021] EWCOP 31 (

I hope Dr N will not think me too pedantic if I make the observation that “patient failed capacity assessment” strikes me as awkwardly expressed. It is not a test that an individual passes or fails, it is an evaluation of whether the presumption of capacity has been rebutted and if so, for what reason.

4. Safeguarding and Mental Capacity

During a safeguarding enquiry, crucial decisions will have to be made at different stages of the process. It is therefore vital that – where an adult does not have mental capacity – decisions made, or action taken on their behalf are in their best interests.

An assessment of an adult’s mental capacity should be considered in all safeguarding cases where:

  • there is a formal diagnosis of cognitive impairment;
  • a neuro-psychological assessment testing suggests they have cognitive impairment;
  • there are concerns about the person’s capacity that have been raised by others;
  • there are discrepancies in the person’s own evaluation of their abilities;
  • there is collateral evidence suggesting a change in their personality;
  • they fail to learn from their mistakes;
  • they repeatedly make risky or unwise decisions.

5. Recording

The two stage test should be used as part of a framework for recording the assessment of mental capacity so that evidence for decision making is clear.

Recording needs to be clear and, where possible, extracts taken from conversations practitioners have had with the adult, to evidence the outcome.

6. Making Decisions on behalf of Someone who lacks Capacity

If, having taken all practical steps to assist the adult to make their own decision, it is concluded that a decision should be made for them, that decision must be made in that person’s best interests. It must also be considered whether there is another way of making the decision which might not affect the person’s rights and freedom of action as much (known as the ‘least restrictive alternative’ principle). See also Promoting Less Restrictive Practice: Reducing Restrictions Tool for Practitioners (ADASS and LGA).

6.1 Decision Makers

Different people can make decisions or act on behalf of someone who lacks mental capacity to make decisions for themselves. The person making the decision is known as the ‘decision maker’, and it is their responsibility to determine what would be in the best interests of the person who lacks mental capacity.

For most day to day actions or decisions, the decision maker will be the carer most directly involved with the person at the time.

Where the decision involves the provision of medical treatment, the doctor or other member of healthcare staff responsible for carrying out the particular treatment or procedure is the decision maker.

Where nursing or paid care is provided, the nurse or paid carer will be the decision maker.

In safeguarding cases, the decision maker will be the person undertaking the enquiry for decisions relating to the safeguarding process and the provision of care and support.

In some cases, the same person may make different types of decision for someone who lacks mental capacity. For example, a carer may carry out certain acts in caring for the person on a daily basis, but if they are also an attorney, appointed under a lasting power of attorney (LPA), they may also make specific decisions concerning the person’s property and financial affairs or health and welfare.

A decision may also, at times, be made jointly by a number of people. For example, when a care plan for a person who lacks capacity is being developed, different healthcare or social care staff might be involved in making decisions or recommendations about their care package. Alternatively, the decision may be made by one practitioner within the team. A different member of the team may then implement that decision, based on what the team has ascertained to be the person’s best interests. Practitioners need to ensure that someone is representing the adult, such as an independent mental capacity advocate (IMCA) or a relevant person’s representative (RPR).

In a best interests meeting, the aim is for everyone involved to be in agreement with the decisions made. However, this may not always be possible.

In such situations, it can be useful to involve different people, for example, to chair the meeting and make decisions, who are separate from the lead practitioner working with the adult.

6.2 Lasting powers of attorney, court appointed deputy and Office of the Public Guardian

A lasting powers of attorney (LPA) allows an adult to appoint an attorney to act on their behalf if they should lose mental capacity in the future. LPAs are registered with the Office of the Public Guardian (OPG).

A court appointed deputy is appointed by the Court of Protection. Depending on the terms of their appointment, deputies can take decisions on welfare, healthcare and financial matters as authorised by the Court of Protection, but they are not able to refuse consent to life sustaining treatment. Deputies are only appointed if the Court cannot make a one off decision to resolve the issues. The OPG supervises deputies appointed by the Court and provides information to help the Court make decisions.

6.3 Independent mental capacity advocates

Independent mental capacity advocates (IMCAs) are those appointed to support a person who lacks capacity but has no one to speak for them. IMCAs have to be involved where decisions are being made about serious medical treatment or a change in the adult’s accommodation where it is provided, or arranged, by the NHS or a local authority. The IMCA makes representations about the person’s wishes, feelings, beliefs and values, and brings to the attention of the decision maker all relevant factors to the case. IMCA services are provided by organisations that are independent of the NHS and local authorities.

6.4 Forward Planning

See Advance Care Planning chapter

Considering the possibility of losing mental capacity and registering lasting power of attorney is usually associated with people getting older. But it is wise to consider such decisions and act on them much earlier in life, in case of unexpected illness or an accident that results in a temporary or permanent loss of mental capacity.

Using an LPA is not limited to circumstances where an adult’s mental capacity is reduced. Due to a physical illness that renders a person (the donor) unable to leave the house for example, an LPA who is registered in relation to property and financial affairs can carry out financial transactions on their behalf and with their permission. In the absence of a registered LPA the alternative would be to borrow the money which could attract charges or to apply to the Court of Protection.

Although an LPA cannot be used until it has been fully registered with the OPG and confirmation received, they can be registered before the adult loses mental capacity which means that they could be used immediately if it should become necessary.

7. Best Interests

See also Best Interests chapter

The Mental Capacity Act sets out a checklist of things to consider when deciding what’s in a person’s best interests. When making best interests decisions, practitioners should:

  • not make assumptions about an adult based on their age, appearance, condition or behaviour;
  • consider all the relevant circumstances;
  • consider whether or when the person has the mental capacity to make the decision;
  • support the person’s participation in any acts or decisions made for them;
  • not make a decision about life sustaining treatment ‘motivated by a desire to bring about his (or her) death’;
  • consider the person’s expressed wishes and feelings, beliefs and values;
  • take into account the views of others with an interest in the person’s welfare, their carers and those appointed to act on their behalf.

9. Excluded Decisions

There are certain decisions which can never be made on behalf of a person who lacks capacity to make those specific decisions. This is because they are either so personal to the individual concerned, or they are governed by other legislation.

Although the Act does not allow anyone to make a decision about the matters below on behalf of someone who lacks capacity to make such a decision for themselves (for example, consenting to have sexual relations), this does not prevent action being taken to protect a vulnerable person from abuse or exploitation.

Decisions concerning family relationships

Nothing in the MCA allows a decision to be made on someone else’s behalf on:

  • consenting to marriage or a civil partnership;
  • consenting to have sexual relations;
  • consenting to a decree of divorce on the basis of two years’ separation;
  • consenting to the dissolution of a civil partnership;
  • consenting to a child being placed for adoption or the making of an adoption order;
  • discharging parental responsibility for a child in matters not relating to the child’s property; or
  • giving consent under the Human Fertilisation and Embryology Act 1990.

Mental Health Act matters

Where a person who lacks capacity to consent is currently detained and being treated under the Mental Health Act 1983, nothing in the MCA authorises anyone to:

  • give the person treatment for mental disorder; or
  • consent to the person being given treatment for mental disorder.

Voting rights

Nothing allows a decision on voting – at an election for any public office or at a referendum – to be made on behalf of a person who lacks capacity to vote.

Unlawful killing or assisting suicide

Nothing in the MCA affects the law relating to murder, manslaughter or assisting suicide.