FAQ - Decision-making

‘Mental capacity’ refers to a person’s ability to make decisions. Whether someone lacks capacity is determined on a decision-by-decision basis. For example, your brother may have the capacity to decide what to eat, but may not have the capacity to decide whether to have an operation or not.

Your brother can’t be labelled as ‘lacking capacity’ in all areas. If someone suggests that your brother ‘lacks capacity’, your next question to them could be ‘lacks capacity for what decision?’

Different laws in the UK countries govern mental capacity:

• In England and Wales this is the Mental Capacity Act 2005
• In Scotland this is the Adults with Incapacity (Scotland) Act 2000
• In Northern Ireland this is the Mental Capacity Act (Northern Ireland) 2016

Read more in our guide on Decision-making here.

You and your family might think of yourselves as ‘next of kin’, but the law doesn’t recognise that next of kin have the right to make decisions for someone else. All adults have the right to make their own decisions wherever possible and mental capacity laws apply to everyone, not just paid carers or professionals.

If a person is unable to make a decision for themselves, the law states that others can act in their ‘best interests’. Your knowledge of your sister will help you judge whether she can make a decision or not. So as long as you are acting in your sister’s best interests, you and your Dad can continue to make most day-to-day decisions on her behalf.

If you want to help your sister manage her benefits, then you can become her appointee. You can apply to become an appointee through the Department of Work and Pensions here, and there is no cost to this. Being an appointee doesn’t cover savings or managing property – for this you would need a different permission.

If you want to help your sister with bigger financial decisions, like managing savings or property, then you will need to apply for permission to do this. The process and the cost of this varies depending on which country you live in:

• In England and Wales, this is called power of attorney or deputyship
• In Scotland, this is called continuing power of attorney or guardianship
• In Northern Ireland, this is called enduring power of attorney or controllership

Find out more:

• Download Sibs guide on Decision-Making here (read page 4 for an overview of mental capacity and pages 6-8 for more detail on the question above)
  

There are different laws in the UK countries that determine the permission you need. Different fees will apply.

• In England and Wales, you can apply to the Court of Protection to be his Health and Welfare Deputy
• In Scotland, you can apply to the Sheriff Court to be his Welfare Guardian
• In Northern Ireland there is no way to give a person legal power to make healthcare decisions on your behalf

Download our guide on Decision-making to find out more.

In terms of improving your brother’s quality of life, start by suggesting activities that you feel he would enjoy. Start small – even everyday things like giving your brother a choice of two different drinks offers him more control over his life. It may be easier for your parents, and your brother, to take an introduction to new things gradually. When you’re talking to your parents about local groups or activities you think he’d like, try and leave some written information or a website for them to re-read and think about. Join our private Facebook community #Siblife to chat with other siblings who have also faced this issue.

Your views are important. You have the lived experience of growing up with your sister. Your parents, family friends and any health or social care professionals involved with your sister’s care haven’t had the same experiences as you and don’t know your sister in the same way. If you have suggestions you would like to share in a decision-making process you can contribute these as an individual in your own right. Any decisions which are made in your sister’s best interests should be made whilst collaborating with those who know her well – including siblings. Let any professionals involved with your sister’s care know that you would like to be involved and to include you in invitations to meetings.

It depends on whether your brother is able to understand the long-term implications of not brushing his teeth:

• If he does – and he still chooses not to – then yes, it is his decision to make
• If he doesn’t – then a best interests decision needs to be made and he needs to be supported in looking after his teeth

You know your brother well and will probably be aware of his ability to understand the long-term consequences. Discuss this with the support workers and see if they can support your brother to brush his teeth in other ways – using a particular paste, brushing to music or doing it at a different time of day. You will be able to give them ideas on what might work and what won’t.

If the support workers are unresponsive to this, contact Adult Social Care for advice. They can carry out a formal mental capacity assessment for your brother. They can hold a meeting with support workers to ensure a new method for supporting your brother to brush his teeth is included in his care plan.

Read more about mental capacity in our guide on Decision-making here.

If you don’t agree with a decision that’s been made, you can ask for a best interests meeting to discuss the situation with staff members. You can give your perspective and ask them to discuss theirs in more detail. Care home staff should be documenting such decisions and be able to justify them.

If you still disagree with the decision, you can make a complaint in writing to the care home manager, clearly stating what you feel your sister’s best interests are in this situation. If you believe that your sister is at risk of neglect or abuse you can contact Adult Social Care to make a safeguarding referral.

Written by Sibs trustee and solicitor, Carol McBride.

Explaining the AGNI Supreme Court decision (2026) and what it means for siblings

In June 2026, the UK Supreme Court handed down an important ruling which fundamentally changes when a disabled person is considered to be “deprived of their liberty” in care settings. The case is commonly referred to as AGNI (as it was brought by the Attorney General for Northern Ireland).

For over a decade, the law had followed an earlier case called Cheshire West which said that a person was deprived of their liberty if their care arrangements entailed continuous supervision, they were not free to leave and there was an element of state involvement —regardless of whether they seemed happy or settled. This meant that many people with disabilities in care homes, hospitals, or supported living were automatically treated as deprived of their liberty and were given legal safeguards (such as formal authorisation, rights to independent review and a route to challenge their care arrangements in the courts).

The AGNI decision has changed this approach in two key ways:

• First, the Supreme Court rejected the old “acid test” referred to in Cheshire West and said that deprivation of liberty must now be assessed using a broader, multi-factor approach. This means looking at the person’s whole situation—such as the type of restrictions, how long they last, and their impact—rather than applying a simple rule.
• Secondly, the Court said that a person can sometimes be treated as consenting to their care arrangements even if they lack formal mental capacity, if their wishes and feelings show they are content.

What this means for people with a disabled brother or sister

For families, this is a very significant shift. Previously, if your brother or sister lacked capacity and was under close supervision, the law would almost always treat them as deprived of their liberty. That triggered safeguards—regular reviews, rights to challenge their placement, and access to advocacy.

Now, some people in exactly the same situations may no longer legally count as deprived of their liberty, especially if they appear settled or do not object.

This can have mixed consequences:

• On one hand, it may mean less bureaucracy and fewer formal legal processes where the person is genuinely happy and well cared for.
• On the other hand, it means fewer automatic safeguards. Some individuals who would previously have had independent oversight of their care may no longer receive those protections. This can also affect their eligibility to legal aid and legal representation.

Why it matters

The law is now less clear-cut and more dependent on interpretation. Whether someone is deprived of their liberty will depend on a detailed, case-by-case assessment rather than a simple test, and it is likely that further case law will follow. Because there was no individual at the heart of the Attorney General’s application to the Supreme Court, there is no route of appeal to the European Court of Human Rights. There is also no ‘grace period’ so professionals are being expected to apply the new test immediately. While the Department of Health and Social Care has offered interim guidance [UK Supreme Court 2026 judgment on what constitutes a deprivation of liberty – GOV.UK] it is likely to take some time for practitioners and families to work through the implications of the ruling.

For siblings, the key impact is that the responsibility may shift more towards families and professionals to actively check that care arrangements are appropriate and sufficiently person-centred.