[Warning: this post contains a legal analysis of the question whether a person can be said to have capacity to take their own life, and is written in response to numerous requests. It is not intended either as an answer to the question as to whether in any given situation that answer is ‘yes,’ or as a discussion of the deep moral, ethical and social conundrums to which such an answer would give rise.]
The final report of the Independent Review for the Mental Health Act 1984 had a concluding section on the future direction of travel – the potential fusion of the Mental Health Act 1983 and the Mental Capacity Act 2005. The report set down a number of ‘confidence tests’ which would need to be met before a fusion project was started, the first being whether fusion had sufficient support from service users (the term used by the report). The report noted that:
During our engagement processes we heard a number of service users outlining a key concern about a capacity-based mental health system, or full fusion. We heard examples of people in distress being told that nothing could be done because “you have capacity, and it’s your choice what you do.” The reasons for this may sometimes be understandable,[footnote] and may represent system or training issues which could be addressed. However, service users will have to decide that being able to make their own decisions about admission is worth the risk of being refused treatment, or being left to do something that is harmful to themselves or others. At the moment we are not convinced that most service users would think this way.
A footnote noted that “[f]or instance, this may be a reaction from overstretched staff (these examples often came from crisis services or A&E) with a very limited or non-existent choice of alternative services.”
The report – here – touched upon two very deep questions: (1) when can a person have capacity to take their own life; and (2) what obligations are imposed upon the state in relation to a person who has expressed an intent to take their own life?
In the abstract, it is clear that the English courts accept that a person can have the capacity to take their own life. This could include both refusing either the starting or the continuing of life-saving treatment (see, for instance Kings College Hospital NHS Foundation Trust v C & Anor  EWCOP 80), or the taking of active steps to bring about their own death (see, for instance, A Local Authority v Z  EWHC 2817 (Fam) – capacity to take the decision to go to Dignitas).
The European Court of Human Rights, similarly, accepts that a person can have this capacity. In Haas v Switzerland  ECHR 2422, for instance, it held that “an individual’s right to decide by what means and at what point his or her life will end, provided he or she is capable of freely reaching a decision on this question and acting in consequence, is one of the aspects of the right to respect for private life within the meaning of Article 8 of the Convention.”
Conversely, however, the ECtHR in the same case emphasised (at paragraph 54) that the Convention must be read as a whole, such that, “in the context of examining a possible violation of Article 8, to Article 2 of the Convention, which creates for the authorities a duty to protect vulnerable persons, even against actions by which they endanger their own lives […]. For the Court, this latter Article obliges the national authorities to prevent an individual from taking his or her own life if the decision has not been taken freely and with full understanding of what is involved.”
In Arskaya v Ukraine  ECHR 1235, the ECtHR found that there had been a breach of Article 2 ECHR where a person, S, repeatedly refused to life-saving treatment in circumstances where “S. showing symptoms of a mental disorder, the doctors took those refusals at face value without putting in question S.’s capacity to take rational decisions concerning his treatment. Notably, if S. had agreed to undergo the treatment, the outcome might have been different […]. the Court considers that the question of the validity of S.’s refusals to accept vitally important treatment should have been properly answered at the right time, namely before the medical staff refrained from pursuing the proposed treatment in relying on the patient’s decision. From the standpoint of Article 2 of the Convention a clear stance on this issue was necessary at that time in order to remove the risk that the patient had made his decision without a full understanding of what was involved.”
The Grand Chamber of the ECtHR confirmed in Fernandes v Oliveira v Portugal  ECHR 106 that “a psychiatric patient is particularly vulnerable even when treated on a voluntary basis. Due to the patient’s mental disorder, his or her capacity to take a rational decision to end his or her life may to some degree be impaired. […], the Court considers that the authorities do have a general operational duty with respect to a voluntary psychiatric patient to take reasonable measures to protect him or her from a real and immediate risk of suicide. The specific measures required will depend on the particular circumstances of the case, and those specific circumstances will often differ depending on whether the patient is voluntarily or involuntarily hospitalised. Therefore, this duty, namely to take reasonable measures to prevent a person from self-harm, exists with respect to both categories of patient. However, the Court considers that in the case of patients who are hospitalised following a judicial order, and therefore involuntarily, the Court, in its own assessment, may apply a stricter standard of scrutiny.”
There are more cases to which I could refer, but these suffice to draw out the key points. 
There is a presumption of capacity enshrined in s.1(2) MCA 2005 but the presumption is not a substitute for an assessment of capacity. Where there is proper reason to think that person may lack capacity to take their own life, it is necessary to carry out a proper assessment of their capacity. Such is clear both from Re Z and also Arskaya. What will count as a proper reason is easier to identify in practice than to address in the abstract. I would not go as far as to say that any expression of an intention to take one’s own life is automatically going to serve as reason to consider that the person lacks the capacity to make the decision. However, especially in any situation where even a partial step has been taken to put that intention into action (for instance, where the consideration is taking place in an A&E department after a person has been brought in after taking an overdose), the default position should be that a proper assessment of capacity should be carried out.
It is also important to emphasise that the determination of capacity is on the balance of probabilities (i.e. more likely than not), and the requirement is for a ‘reasonable belief’ (on the basis of ‘reasonable steps’ having been taken to establish) that the person lacks capacity to consent to acts of care and treatment being carried out. Especially in a fast-moving situation where professionals have limited information, and in circumstances where not taking action could endanger the person’s life, the threshold for concluding that the person lacks capacity to decide whether or not to take their own life (or, by refusing medical treatment, to prevent reversal of steps they have already taken) is going to be low. Put another way, and using the language of Arskaya, medical professionals must make sure that they have “properly answered” the question of whether steps being taken by the person before they refrain from taking the necessary steps in relying upon the person’s decision.
There is an important caveat to what I have set out above, which is directing professionals to be more ready to take steps in the name of the person’s best interests than they might sometimes feel comfortable with. That is that, as they have more time in which “properly to answer” the question of the person’s capacity, they must be willing to reconsider their assessment. Such calibration is necessary to ensure the right line is trodden between on the one hand the positive obligations imposed by Article 2 ECHR and the right to autonomy enshrined in Article 8 ECHR.
Finally, and whilst it is increasingly (and rightly) being seen as important to assess a person’s capacity to make relevant decisions in the context of considering admission under the MHA, capacity must never be used against the person. In this context, it is always potentially concerning to hear of situations where it appears that a person’s request for assistance (including by way of admission to mental health hospital) because they fear that they may take their own life has been treated – in Catch-22 fashion – as evidence that they have capacity to make that decision, and hence a ground for not admitting the person. To reiterate, the critical question is whether the person, at that point, is at real and immediate risk of suicide – if they are, then the state’s operational duty under Article 2 is very likely to be engaged; depending upon the circumstances, it may well be that the way in which to discharge that duty is to admit them to hospital. In such a situation, the person’s decision-making capacity will be relevant not to the question of whether to admit, but whether they can be admitted as an informal patient or by way of formal admission for assessment or treatment.
 I am talking here about ‘real-time’ consideration of capacity, rather than the question at an inquest of whether a verdict of suicide can be returned, at which point the question is whether, on the balance of probabilities, the person deliberately took their own life intending to kill themselves: see R (Maughan) v Senior Coroner for Oxfordshire  EWCA Civ 809.
 “Real and immediate risk” is a phrase that is routinely used in this context, “real” means more than remote or fanciful; “immediate” means “present and continuing”: see Rabone & Anor v Pennine Care NHS Foundation Trust  UKSC 2 at paragraphs 38-41.
 I do not address here the implications of the Convention on the Rights of Persons with Disabilities or the approach adopted by the (former) constitution of the Committee towards the concept of mental capacity. The annex to the report of the Independent Review of the MHA 1983 provides an outline of the considerations; also of relevance is the change of stance manifested by the (new) Committee’s approval of the Australian Law Reform Commission’s approach, which considers that “art 17 of the CRPD may require the representative to make a decision that protects the person’s ‘physical and mental integrity’, notwithstanding the decision conflicts with the person’s expressed will and preferences. A qualification of this kind tests the limits of autonomy, particularly where the limitation concerns harm to oneself. Examples are seen usually in the context of mental health legislation: to save a patient’s life, or to prevent a patient from seriously injuring themselves or others. Safeguards may be included in terms of ensuring that the course of action proposed is the ‘least restrictive’ option.”
 I should emphasise that from the reports of such interactions it appears that more may well be going on beneath the surface, which raises the separate issue of communication.