Mental Capacity Act 2005

The MCA 2005 codified previous common law principles into a comprehensive framework. The five principles in section 1 are: presume capacity, support decision-making, unwise decisions are not incapacity, best interests, least restrictive option. Section 2 defines incapacity as inability to make a decision because of an impairment of, or disturbance in, the functioning of the mind or brain. The Court of Protection makes decisions for those who lack capacity. LPAs (registered with the Office of the Public Guardian) allow proactive appointment of decision-makers. Deprivation of Liberty Safeguards, which the Liberty Protection Safeguards were intended to replace before implementation was deferred, protect those deprived of liberty in their best interests.

In practice, the Act is applied through a two-stage test that professionals are supposed to work through in order. First, is there an impairment of or disturbance in the functioning of the mind or brain? Second, does that impairment mean the person cannot do one of four things: understand the relevant information, retain it long enough to decide, use or weigh it, or communicate the decision? Both stages must be satisfied, and there must be a causal link between them. Capacity is assumed until the contrary is shown, and the burden sits on whoever asserts that it is absent.

Worked example: Eleanor has vascular dementia and wants to stay in her own home despite two recent falls. The social worker assesses her capacity to decide where to live. Eleanor understands she has fallen and that she might fall again, but she cannot retain or weigh the risk from one conversation to the next. That amounts to a lack of capacity for that specific decision. It says nothing about her capacity to manage her daily spending, to consent to a flu vaccination, or to decide who visits her — each must be assessed separately when the decision arises. Because she lacks capacity about her residence, any move must be a best interests decision, made in the least restrictive way and with her long-held wish to remain at home given real weight.

The misconceptions cause real harm. A diagnosis is not a finding of incapacity, and an unwise decision is not evidence of it — the Act expressly protects the right to make choices others think foolish. Capacity is not a permanent label: it fluctuates, and assessments must be repeated. Family members have no automatic authority to decide for an adult; only a registered attorney or a court-appointed deputy does. And an assessment carried out without first offering practical support — the right time of day, plain language, an interpreter, visual aids — is defective.

The Act creates the best interests framework, the lasting power of attorney, the Court of Protection, DoLS, and the IMCA role. Read our guides to the Mental Capacity Act and lasting powers of attorney — putting an LPA in place while you have capacity avoids most of these problems.