Author and Publication
Author: Nellie Supports Ltd
Publication Date: 15/05/2026
Citation
Mental Capacity Act 2005, c. 9. Available at: https://www.legislation.gov.uk/ukpga/2005/9/contents
Copywright
Copyright © 2026 Nellie Supports Ltd. All rights reserved.
This article is made available for general information, education and professional reference. It may be downloaded, printed and shared for non-commercial purposes, provided that it is reproduced in full, is not altered in any way, and is properly cited as the work of Nellie Supports Ltd. This material must not be edited, adapted, sold, republished, incorporated into commercial products, or used for commercial training, assessment, report-writing or advisory services without prior written permission from Nellie Supports Ltd.
This article does not constitute legal advice, clinical advice or a substitute for a decision-specific professional assessment. Where legislation, government guidance, court forms or external professional materials are referred to, those materials remain subject to their own copyright, licensing and re-use terms.
What duties must a trustee understand?
A trustee must broadly understand the duties the office carries: to act in accordance with the trust's terms; to act in the interests of the beneficiaries as a whole; to exercise reasonable care and skill; to avoid conflicts between personal interest and the trust; not to profit from the position; to invest and manage trust property prudently; and to keep accounts and inform beneficiaries appropriately. Capacity to act as a trustee requires broad understanding of these duties and the ability to apply them to the trust's actual decisions, not the recall of trust law chapter and verse. This guide explains each duty at the level the capacity test actually requires.
The office is defined by its duties
Asking what duties a trustee must understand is really asking what the office consists of, because a person cannot have capacity to hold an office they cannot comprehend. The duties are the relevant information for trusteeship: that the property is held for others, that the terms of the trust govern what may be done, that beneficiaries must be treated properly and that the trustee must not turn the position to their own advantage. A trustee need not recite trust law, but they must grasp these obligations in working, practical terms.
The duty to act within the terms of the trust
The first duty is obedience to the trust itself: the trustee must understand that the trust document sets the rules, that the property must be dealt with as the trust directs and that they cannot simply do what seems sensible or generous to them personally. In assessment, this is tested through the person's own account of what the trust is for and what it permits, and a trustee who describes the trust property as effectively their own to direct has failed to grasp the duty that defines everything else.
Duties to the beneficiaries
The trustee must understand who the beneficiaries are, that decisions are made in their interests and, where there is more than one beneficiary or class, that they must be held in fair balance rather than one preferred because the trustee likes them better. Family trusts test this duty hardest, because the trustee is frequently a parent, sibling or step-parent of the very beneficiaries whose competing interests must be balanced, and the assessment should explore whether the person can separate the office from the relationships.
The duty of care in managing trust property
The trustee must understand that trust assets require active, prudent stewardship: property maintained and insured, money applied properly, advice taken where the trustee lacks the expertise, and records kept of what was done and why. The person does not need investment expertise of their own, but they must recognise that neglect is itself a breach, and that signing whatever is put in front of them without understanding it is not the exercise of the office but the abandonment of it.
The duty of loyalty: no profit, no conflict
The trustee must grasp that the position cannot be used for their own benefit: no unauthorised profit, no purchasing trust property for themselves, no placing themselves where duty and personal interest collide without proper authority. In capacity terms this duty is revealing, because a trustee who can no longer perceive the boundary between trust money and their own, or who cannot see why a transaction benefiting themselves is even a question, is displaying exactly the loss of understanding the assessment exists to detect.
Understanding proportionate to the trust
As with property transactions, the required understanding scales with what the office actually demands. A bare trustee of a single property awaiting sale must understand comparatively little; a trustee of a discretionary settlement with investments, competing classes of beneficiary and tax consequences must understand far more. The assessment should therefore begin with the actual trust, identify what this office genuinely requires of this trustee and calibrate the relevant information accordingly, rather than testing every trustee against an imagined standard.
How understanding of the duties is tested
The duties are tested through the trustee's own words: whose property is this, who is it for, what does the trust let you do with it, how would you decide between the beneficiaries, what would you do if a proposed step benefited you personally. Scenarios drawn from the trust's real circumstances work far better than abstract questions, and revisiting the same ground later in the conversation tests whether the understanding is held or merely echoed. The person's answers, recorded verbatim, become the core of the evidence.
What the assessment and report should record
The report should set out the trust and its practical demands, the duties identified as the relevant information, the practicable steps taken, the trustee's own explanations, the functional analysis against understanding, retaining, using or weighing and communicating, and the causative link to any impairment found. It should conclude on the office and decisions actually assessed, so that co-trustees, advisers and, where necessary, the court can act upon it with confidence in exactly what it does and does not establish.
Key takeaway
A trustee must understand the four pillars of the office: the trust's terms govern, the beneficiaries come first, the property demands prudent care and the position must never serve the trustee's own interest. Test those duties against the real trust in the trustee's own words, calibrate the depth to what the office actually demands and record the answers, because the duties are the office, and understanding them is the capacity in question.
Frequently asked questions
Does a diagnosis automatically mean someone lacks capacity?
No. A diagnosis may explain why capacity is in doubt, but it does not answer the legal question. The assessment must still consider the specific decision, the relevant information, the support provided and whether the person can understand, retain, use or weigh that information and communicate a decision.
What evidence is useful for Capacity to Act as a Trustee?
The trust deed and a plain account of what this trusteeship involves in practice: the assets, the beneficiaries and the decisions that recur. The assessor tests the person's grasp of the duties as they bear on those real decisions.
When is a formal assessment for Capacity to Act as a Trustee useful?
Assess formally when a trustee's grasp of their duties is genuinely doubted and decisions are pending, particularly investment changes, distributions or dealings with land, where an invalid trustee act creates problems for everyone downstream.
Related mental capacity assessment pages
These internal links help readers move from this guide to the most relevant Nellie Supports service page, assessment option or legal framework page.
Duties and capacity needing evidence?
Nellie Supports completes trustee capacity assessments across England and Wales, addressed to the trustee functions in question, with a same working day response and every report peer reviewed before delivery. Call 0333 987 5118 or visit the trustee capacity service page.