Skip to content 
Stamp duty land tax is one of the most significant upfront costs in any property transaction, and the difference between paying residential rates and non-residential rates can run to tens of thousands of pounds on a single purchase. It is no surprise that buyers and their advisers look carefully at which set of rates applies — but a recent Court of Appeal decision has made it considerably harder to argue for non-residential treatment than it once was. Our tax advisors at Tax Accountant work with property buyers, landlords and investors on SDLT planning and compliance, and this is an area where getting the classification wrong can result in a substantial unexpected liability.
How SDLT Works and Why the Classification Matters So Much
Stamp duty land tax applies to the acquisition of a chargeable interest in land in England and Northern Ireland. The buyer is liable, and the amount is based on the chargeable consideration paid. What determines the rate, however, is whether the property being acquired is classified as residential or non-residential — and the gap between those two sets of rates is very wide indeed.
For residential property, the rates rise progressively and can reach 12% on the portion of the purchase price above £1.5 million. On top of that, an additional 3% surcharge applies if the property is an additional dwelling, and a further 2% applies if the buyer is not resident in the UK. For non-residential property, the maximum rate is just 5%. HMRC’s guidance on SDLT rates for non-residential and mixed use land sets out those rates clearly.
On a purchase price of £1.75 million, the difference between the two rate structures can easily exceed £100,000. That is the size of the financial incentive that drives buyers to explore whether any element of non-residential use can be established in their acquisition.
The Legal Definition of Residential Property
The definition of residential property for SDLT purposes comes from Finance Act 2003, section 116. Under subsection (1)(a), residential property means a building that is used or suitable for use as a dwelling, or is in the process of being constructed or adapted for such use. The residential rates apply where the land being acquired is comprised entirely of residential property. Non-residential rates apply where the land does not consist entirely of residential property — meaning even a small element of genuine non-residential use can shift the entire transaction into the lower rate band.
The critical word in the definition is “suitable.” A building does not need to be in use as a dwelling at the point of purchase to be classified as residential. It only needs to be suitable for use as one. This distinction has been at the heart of a significant volume of SDLT litigation over recent years, with buyers arguing that the condition or state of a property meant it was not suitable for use as a dwelling on the date of completion.
What the Mudan Case Means for Buyers
The Court of Appeal decision in Mudan and Anor v HMRC [2025] EWCA Civ 799 has gone a long way to settling how this question should be approached, and the answer is not favourable to buyers seeking non-residential treatment.
In that case, the Mudans purchased a London property in 2019 for £1,755,000 and initially paid £177,000 in SDLT on the basis that it was residential. They subsequently amended their return, arguing the property was not suitable for use as a dwelling due to its condition and seeking to reduce their liability to £77,250. HMRC disagreed, maintaining that the property was suitable for use as a dwelling on the effective date of the transaction.
The Court of Appeal confirmed that a building which was recently used as a dwelling, has not been adapted for another use in the interim, and is capable of being used as a dwelling again will be treated as a dwelling — even if it is not ready for immediate occupation. The court acknowledged that a sufficient degree of disrepair could in principle take a property outside the definition, but made clear that the threshold is high. Relatively minor or even moderately significant disrepair is not enough. The property needs to be in a condition that genuinely prevents it from functioning as a dwelling, not simply one that requires renovation or repair before it would be comfortable to live in.
The practical consequence of this decision is that arguing non-residential treatment on the basis of a property’s condition has become significantly harder. HMRC is increasingly unlikely to accept that a property falls outside the residential definition unless the facts are exceptional — and most buyers should proceed on the assumption that a recently used residential building will be treated as residential for SDLT purposes regardless of its current state of repair.
Where Non-Residential Treatment Can Still Apply
This does not mean non-residential or mixed-use treatment is never available. There are genuine cases where a property being acquired includes a clear non-residential element — a commercial unit attached to a residential building, land with agricultural use, outbuildings used commercially, or a property that has genuinely been adapted and used for non-residential purposes and has not functioned as a dwelling for a significant period.
In those situations, the non-residential rates can legitimately apply, and the tax saving can be very substantial. The key is that the non-residential element must be genuine and evidenced, not constructed or overstated to achieve a tax outcome. HMRC is scrutinising these claims with increasing rigour, and the post-Mudan landscape means that condition-based arguments in particular are likely to fail at enquiry stage.
Our tax advisors can review the facts of a proposed acquisition before completion to give you a clear view of how SDLT is likely to apply and whether any legitimate basis for mixed-use or non-residential treatment exists. This kind of pre-transaction advice through our property income tax service is considerably more useful than discovering a problem after the return has been filed.
SDLT and the Additional Dwellings Surcharge
For buyers acquiring an additional residential property — whether as a buy-to-let investment, a second home or otherwise — the 3% surcharge applies on top of the standard residential rates. This surcharge significantly increases the cost of acquiring investment property and is another reason why the residential versus non-residential question is so commercially important.
Where a buyer is replacing a main residence, the surcharge may not apply or may be refundable in certain circumstances. The rules around this are detailed and time-sensitive. HMRC’s guidance on the higher rates for additional dwellings explains the conditions and timeframes that apply.
Our team handles SDLT compliance and planning as part of our wider personal tax services and can advise on whether the surcharge applies to your specific purchase and whether any reliefs or exemptions are available.
SDLT Relief and the Risk of Getting It Wrong
SDLT is a self-assessed tax. The buyer completes and submits the return, and the liability is calculated on the basis of the information provided. Where a return takes a position that HMRC later challenges — such as applying non-residential rates to a property HMRC considers residential — the buyer faces not only the additional SDLT but potentially interest and penalties on the underpaid amount as well.
The Mudan case illustrates this precisely. The Mudans initially paid the full residential SDLT liability, then filed an amended return claiming non-residential treatment and a lower rate. HMRC challenged the amended position and, following the Court of Appeal decision, the original liability was upheld. Buyers who amend returns on the basis of arguments that do not meet the legal threshold are exposed to exactly this kind of outcome.
Taking proper tax advice before filing — not after — is the point at which a specialist tax consultant genuinely adds value. If there is a legitimate argument for a lower rate, that argument needs to be properly grounded in the facts and supported by evidence. If the argument is weak, it is better to know that before submitting the return than to face a challenge from HMRC further down the line. The ICAEW has published useful technical commentary on SDLT and property transactions for those who want a deeper professional perspective on where the boundaries currently sit.
How Our Tax Advisors Can Help
SDLT is an area where the stakes are high and the rules are more nuanced than they appear on the surface. Whether you are buying a property and need to understand which rates apply, reviewing whether a previous return was filed correctly, or dealing with an HMRC enquiry into an SDLT position, our team can help you navigate the position with clarity.
We advise on SDLT as part of our tax planning and advisory service and our specialist tax services, including where HMRC has opened a compliance check or is questioning the basis on which a return was submitted. If you are in the process of acquiring property and want to understand your SDLT position before you complete, get in touch with our team and we will work through the facts with you.
This article is for general guidance only and does not constitute personal tax advice. Individual circumstances vary. Please speak to a member of our team for advice tailored to your specific situation.