Part of: UK Council Tax 2026 — Complete Guide → Council Tax Disability Help 2026 — DBRS, SMI, Carer Discount Guide
TL;DR: Severely mentally impaired (SMI) persons are disregarded for Council Tax purposes. If all adult residents at a property are SMI, the property is fully exempt under Class U (zero Council Tax). If some but not all residents are SMI, the SMI person is individually disregarded, potentially enabling the Single Person Discount. The exemption requires a GP certificate AND a qualifying disability benefit. Around 30% of eligible households do not claim.
Last reviewed: 27 April 2026
The SMI Definition
The severely mentally impaired (SMI) status for Council Tax purposes is defined in the Council Tax (Discount Disregards) Order 1992. A person qualifies as severely mentally impaired where they have a severe impairment of intelligence and social functioning, however caused, that appears to be permanent.
The condition must be:
- Severe in its impact on intelligence and social functioning - not a mild impairment
- Apparently permanent - the condition is not expected to resolve, even if there may be fluctuation in severity
The cause is irrelevant. SMI status can arise from:
- Dementia (Alzheimer's disease, vascular dementia, Lewy body dementia, frontotemporal dementia)
- Severe learning disabilities (Down's syndrome at the more severe end, profound intellectual disability from other causes)
- Severe stroke effects with significant and permanent cognitive and functional impairment
- Huntington's disease - progressive neurological condition with cognitive involvement
- Severe Parkinson's disease - in advanced stages with significant dementia component
- Severe traumatic brain injury with permanent cognitive effects
- Severe autism with accompanying intellectual disability at the higher end of the spectrum
- Multiple sclerosis in advanced stages with permanent cognitive involvement
The Dual Test: Both Conditions Must Be Met
The definition requires two conditions to be satisfied simultaneously:
Condition 1 - Medical certification: A registered medical practitioner (typically the person's GP or a specialist such as a consultant psychiatrist, neurologist, or geriatrician) certifies that the person has a severe and apparently permanent impairment of intelligence and social functioning.
Condition 2 - Qualifying benefit receipt: The person must be entitled to one of the following:
- Attendance Allowance (either rate)
- Disability Living Allowance (DLA) - care component at middle or highest rate
- Personal Independence Payment (PIP) - daily living component at standard or enhanced rate
- Employment and Support Allowance (ESA) - support group component
- Universal Credit - Limited Capability for Work and Work-Related Activity (LCWRA) element
- Severe Disablement Allowance (legacy benefit)
- Incapacity Benefit (legacy benefit, still in payment for some long-term recipients)
- Constant Attendance Allowance (under industrial injuries or war pensions schemes)
- Armed Forces Independence Payment (AFIP)
"Entitled to" means that the benefit has been awarded - not merely that the person would likely qualify if they applied. Many SMI persons have not applied for the qualifying benefit, which prevents the disregard from applying even though the medical condition itself clearly meets the SMI test.
Class U Exemption vs the SMI Disregard
The SMI provisions operate differently depending on the household composition:
Class U (100% exemption): Applies when every adult resident at the property is severely mentally impaired. Zero Council Tax is payable. The Class U exemption is found in the Council Tax (Exempt Dwellings) Order 1992.
SMI Disregard (partial relief): Applies when some but not all adult residents are SMI. The SMI persons are individually disregarded - effectively not counted for Council Tax purposes. This can enable the Single Person Discount (25% off) if the SMI disregard leaves only one non-disregarded adult.
Example 1: An elderly woman with advanced dementia lives alone. She receives Attendance Allowance. Her GP certifies SMI. All residents are SMI. Class U applies. Council Tax: £0.
Example 2: An elderly man with dementia lives with his spouse (who is not SMI). He receives Attendance Allowance. His GP certifies SMI. He is disregarded under the SMI disregard. His wife is the sole non-disregarded adult. Single Person Discount (25% off) applies.
The Under-Claim Problem
The IRRV (Institute of Revenues, Rating and Valuation) and disability awareness organisations have consistently highlighted that the SMI exemption and disregard are significantly under-claimed.
Conservative estimates, drawing on Alzheimer's Society awareness campaign data and IFS local government finance research, suggest that approximately 30% of households that would qualify for SMI relief are not claiming it. This represents hundreds of thousands of eligible families paying Council Tax they do not owe.
Common reasons for under-claiming:
- Families managing a dementia diagnosis or brain injury are focused on care, not Council Tax administration
- The dual test (medical certificate AND qualifying benefit) is not widely known
- GPs do not routinely advise families to claim the Council Tax SMI disregard
- The billing council does not proactively identify eligible households
- Families assume the disregard has already been applied (it has not - it must be actively claimed)
How to Apply
Step 1: Obtain a medical certificate. Ask the person's GP or consultant to certify that the person has a severe and apparently permanent impairment of intelligence and social functioning. The GP should confirm:
- The underlying condition (dementia, learning disability, brain injury, etc.)
- That the impairment is severe
- That it appears to be permanent
Step 2: Obtain the benefit award letter. Locate the current award letter for the qualifying benefit (Attendance Allowance, PIP, DLA, ESA, or similar). If not yet awarded, apply to DWP for the benefit before or alongside the Council Tax application.
Step 3: Apply to the billing council. Most councils have an online SMI exemption or disregard application form. Submit the GP certificate and the benefit award letter.
Step 4: The council processes the application and adjusts the Council Tax account. The adjustment is backdated to the qualifying date.
Applying When the Person Lacks Capacity: LPA and Deputyship
Many SMI individuals cannot manage their own affairs. Applications on their behalf can be made by:
Attorney under Lasting Power of Attorney (LPA) - property and financial affairs: Registered with the Office of the Public Guardian. The attorney can apply to the billing council directly, providing the LPA documentation, the GP certificate, and the benefit award letter.
Court of Protection Deputy: A deputy appointed by the Court of Protection for property and financial affairs has the same authority.
Family member or carer with council's cooperation: In practice, many billing councils accept applications from close family members or carers acting on behalf of the SMI person, particularly where the GP certificate and benefit award letter are provided and the family member can demonstrate they are acting in the person's best interests.
Backdating: More Generous Than Most Council Tax Relief
The billing council can backdate the SMI disregard or Class U exemption to the date when both conditions were first met (medical certification and qualifying benefit receipt). For most Council Tax reliefs, backdating is limited to 12 months or less.
For SMI, the IRRV guidance acknowledges the significant under-claim problem and encourages councils to backdate to the earliest eligible date the evidence supports. In practice, many councils will backdate up to 6 years (the standard civil limitation period) where clear evidence shows the conditions were met earlier.
For families who discover the relief has not been claimed for many years, a backdated claim can produce a substantial refund or credit.
Backdating the SMI Disregard: How Far Back Can You Claim?
For most Council Tax reliefs, backdating is limited to 12 months or sometimes 3 months. The SMI disregard is treated more generously by many billing councils, recognising the significant under-claim problem.
The IRRV (Institute of Revenues, Rating and Valuation) guidance to billing councils acknowledges that the SMI disregard is one of the most significantly under-claimed Council Tax reliefs. Where a family can demonstrate that both conditions (medical certification and qualifying benefit) were met at an earlier date, many councils will backdate to the earliest evidenced date.
In practice, some councils backdate SMI relief up to 6 years - the standard civil limitation period - where clear evidence supports the earlier eligibility. The billing council calculates the overpayment from the backdated date and either refunds it or applies it as a credit to the current account.
If the SMI person is deceased, the estate's representative (executor or administrator) can still claim a retroactive SMI disregard for the period when the deceased was alive and the conditions were met, subject to the limitation period.
Frequently Asked Questions
My father has dementia - does he automatically get the SMI discount?
No. The SMI disregard must be actively applied for. It is not applied automatically by the billing council. Contact the council, obtain a GP certificate, provide the qualifying benefit award letter, and submit the application. Once applied, the disregard reduces or eliminates the Council Tax, and backdating to the date the conditions were first met is typically available.
My mother has dementia but hasn't applied for Attendance Allowance - does the SMI disregard still apply?
No. The SMI dual test requires both the GP certificate AND a qualifying benefit award. Without an Attendance Allowance (or other qualifying benefit) award, the disregard cannot apply even if the medical condition clearly meets the SMI standard. Apply for Attendance Allowance from DWP first (or simultaneously), then apply for the Council Tax disregard once the AA award is confirmed.
We found out about the SMI disregard 3 years late - can we get money back?
Yes, in most cases. The SMI disregard can be backdated to the date both conditions were first met. Gather evidence of when the GP certificate would have applied and when the qualifying benefit was first awarded. Contact the billing council, explain the situation, and request backdating. With clear evidence, most councils will backdate 3 years or more.
My husband has a severe learning disability but works part-time - does SMI still apply?
Yes. Employment does not disqualify SMI status. The test is the severity of the impairment of intelligence and social functioning, not whether the person works. A person with severe learning disabilities who is in supported employment can still qualify for the SMI disregard if the GP or specialist confirms severe and permanent impairment.
We hold an LPA for our grandmother who has dementia - how do we claim on her behalf?
Provide the billing council with the registered LPA documentation (showing the LPA is registered with the Office of the Public Guardian), the GP or specialist certificate confirming severe mental impairment, and the qualifying benefit award letter (Attendance Allowance or similar). Most councils are familiar with LPA-based applications for the SMI disregard.
How we verified this
The SMI definition, dual test, and qualifying benefit list are from the Council Tax (Discount Disregards) Order 1992. The Class U exemption is from the Council Tax (Exempt Dwellings) Order 1992. The Mental Capacity Act 2005 governs LPA and deputyship. DWP publishes guidance on Attendance Allowance, PIP, and ESA. The under-claim estimate is from IRRV practitioner guidance and Alzheimer's Society awareness campaign data. MHCLG annual statistics document SMI exemption volumes. The IFS has published analysis on under-claiming of disability-related Council Tax reliefs.
Sources & Verification
- Council Tax (Discount Disregards) Order 1992: https://www.legislation.gov.uk/uksi/1992/548/contents
- Council Tax (Exempt Dwellings) Order 1992 (Class U): https://www.legislation.gov.uk/uksi/1992/558/contents
- Mental Capacity Act 2005: https://www.legislation.gov.uk/ukpga/2005/9/contents
- DWP Attendance Allowance: https://www.gov.uk/attendance-allowance
- MHCLG Council Tax guidance: https://www.gov.uk/government/collections/council-tax-statistics
- IFS (Institute for Fiscal Studies): https://ifs.org.uk/
- IRRV (Institute of Revenues, Rating and Valuation): https://www.irrv.net/
This article is for informational purposes only and does not constitute legal, financial, or tax advice. Council Tax rules vary by local authority and change annually. Always verify current rates and rules with your local council and gov.uk before making any decision.
