As a planning solicitor, I routinely work with property developers and private individuals looking to navigate the complex world of planning enforcement. A common point of discussion is the window of time local planning authorities have to take action against a breach.
Personally, I’ve always believed that enforcement windows should align more closely with standard civil court time limits, however, I can understand the rationale behind the new time limits introduced April 2024. Local authorities face massive budget shortfalls, and a ten-year window strikes a realistic, practical balance. It gives resource-strapped councils enough time to become aware of unauthorised developments, assess their impact on the local community, and make a reasoned decision on whether it is genuinely in the public interest to enforce against them.
A recent High Court judgment has brought this exact issue into sharp focus, settling a long-standing debate on Houses in Multiple Occupation (HMOs) and planning immunity.
1. The Outcome of the Case
The case in question is Sentinel Estates Ltd v Secretary of State for Housing, Communities and Local Government & Anor [2026] EWHC 1122 (Admin), handed down on May 12, 2026.
The case centred around a property in Wembley where the London Borough of Brent issued an enforcement notice against Sentinel Estates for turning two self-contained flats into a single HMO without planning permission. Brent argued the council had ten years to take enforcement action. Sentinel appealed all the way to the High Court, arguing that because the property was used for residential living, it qualified for a shorter, four-year immunity window.
The High Court decisively dismissed Sentinel’s appeal. The court ruled that changing the use of a building to an HMO does not benefit from a shorter enforcement window for “single dwellinghouses” and is strictly subject to the 10-year rule.
2. The Previous Unsurety About What Constitutes a ‘Single Dwellinghouse’
To understand why this case went all the way to the High Court, you have to look at how the law was written. Historically, under Section 171B(2) of the Town and Country Planning Act 1990, a shorter four-year enforcement limit applied to a material change of use of a building to “use as a single dwellinghouse.”
For years, there was an exploitable grey area in planning law. Landlords and developers looked at past case law (like Van Dyck) and argued that if a group of unrelated occupiers lived together in an HMO, sharing a kitchen and living like a “single household,” the building functionally operated as a “dwellinghouse.” Landlords frequently used this ambiguity to argue that unless enforcement action was taken against their unauthorised HMO within four years, it automatically gained permanent immunity from council enforcement.
3. The Importance of This Case
The Sentinel Estates decision is incredibly important because it officially slams the door on that argument.
The High Court dissected the exact phrasing of the statute. The judge noted that while an HMO might broadly be considered a residential “dwelling” in some legal contexts, the word “single” is the crucial separator. A “single dwellinghouse” implies a single-household unity (like a family or a single occupant). By definition, an HMO involves multiple or multi-occupation, which directly contrasts with the concept of a single dwellinghouse.
For practitioners and developers, this establishes a definitive legal precedent: Unauthorised HMO conversions do not, and did not, qualify for the four-year rule.
4. Why I Consider the Outcome Correct and Logical
From a legal and practical standpoint, the High Court’s decision is entirely correct and logical.
An HMO has a vastly different footprint on a local community than a standard family home or a pair of flats. It introduces higher density, increased pressure on local infrastructure, more waste production, etc. As such it a longer period of time is required to consider its impact. Further to this, converting a property to a HMO’s is often undertaken with the aim of making a profit. It is logical for development which is profit driven to be subject to a longer window than development undertaken by individuals to benefit that same individual.
5. Why This Doesn’t Matter Anymore (The Universal 10-Year Rule)
While Sentinel Estates provides fantastic clarity on historical cases, there is a major postscript that developers and individuals need to know: for any new developments, this specific debate is officially obsolete.
Under the Levelling-up and Regeneration Act 2023, the old “four-year rule” for changes of use to a single dwellinghouse and operational development was completely abolished. For any planning breaches that were not already substantially completed, a universal 10-year enforcement rule took effect as of 25 April 2024.
This means that whether you are building an extension, or creating an HMO, the council has a full decade to take enforcement action against you. The only exception now is if a developer can prove their project was entirely complete before the transitional cutoff date, allowing them to rely on the legacy rules.
Need advice on a planning issue? Whether you are looking to regularise an existing property use via a Certificate of Lawfulness or need to defend against an enforcement notice, navigating these strict timeframes requires expert legal strategy. Get in touch today to discuss your project.