HMO Conversion in London: The Complete 2026 Planning Guide
Converting a house into a House in Multiple Occupation (HMO) is one of the few moves in London property that can transform the income and value of the same building — and one of the easiest to get wrong. The rules are not London-wide: they change at borough boundaries, they have changed fast in the last eighteen months, and the most expensive mistakes happen before a planning application is ever made.
This is the complete 2026 guide: whether you need planning permission, what it costs, what standards decide approval, and how the regulatory map is moving. Every borough position stated here was verified against council sources in June 2026 — worth saying, because much of what ranks on this subject is out of date.
First principles: what counts as an HMO
A small HMO (Use Class C4) is a dwelling shared by 3–6 unrelated people who share facilities such as a kitchen or bathroom. A single household (a family, a couple) is Class C3. Under national permitted development rules (GPDO Class L), you can switch between C3 and C4 without planning permission — unless the borough has removed that right with an Article 4 Direction.
Above six occupants the property becomes a large (sui generis) HMO, and that change of use always needs planning permission, in every borough, Article 4 or not. This is the single most misunderstood line in HMO conversations.
The second most misunderstood: planning and licensing are different regimes. An HMO licence does not grant or imply planning permission, and being "Article 4-free" never means "no regulation" — mandatory licensing applies across England to HMOs of 5+ people, and most London boroughs now layer additional or selective licensing on top.
The Article 4 question — London's real HMO map
Whether your conversion needs planning permission comes down to one check: does the borough have a C3→C4 Article 4 Direction covering your property? As of June 2026, 22 of London's 33 planning authorities — two-thirds — do, in whole or in part. The map splits three ways:
Borough-wide (17): planning permission is always required. Barking & Dagenham, Barnet, Bexley, Bromley, Croydon, Ealing*, Enfield, Greenwich, Hillingdon, Hounslow, Lewisham, Merton*, Newham, Redbridge, Sutton, Tower Hamlets and Waltham Forest. (Ealing excludes Perivale ward, covered earlier by an immediate direction, and the OPDC area; Merton's final 13 wards came under an immediate direction in March 2026 that is still awaiting formal confirmation.) In these boroughs the work is a full change of use application — assessed on concentration/clustering policies, accommodation standards, amenity and parking. Our Enfield checklist shows exactly what that assessment looks like.
Area-based (5): it depends on the address.Brent (near borough-wide, but with Growth Area and Park Royal exclusions), Haringey (most of the east of the borough), Havering (all dwellings in four wards; elsewhere only flats, terraced and semi-detached homes — detached houses retain PD rights), Lambeth (two Streatham wards, since August 2025) and Southwark (two specific streets). Here the first step is always a site-specific check against the council's Article 4 map — one street can sit on the opposite side of the line from the next.
Article 4-free (11): permitted development still applies. Camden, the City of London, Hackney, Hammersmith & Fulham, Harrow, Islington, Kensington & Chelsea, Kingston, Richmond, Wandsworth and Westminster. In these boroughs a small HMO conversion needs no planning application — but two big caveats follow.
First, protect the position before you rely on it. A Lawful Development Certificate (Proposed) is the formal confirmation that your specific conversion is lawful permitted development — inexpensive insurance before committing to a purchase, and proof of lawful use forever after.
Second, the free list is shrinking. Sutton went borough-wide in February 2025, Lambeth designated its Streatham wards in August 2025, Ealing went borough-wide in November 2025, Hillingdon in December 2025, Merton completed its coverage in March 2026 — and Hammersmith & Fulham has approved a borough-wide direction (expected to take effect around a year after it is made), while Harrow has an immediate direction in the pipeline that could arrive with no notice period. Landlords already operating C4 HMOs in newly-designated boroughs should secure an LDC (Existing) to evidence their established use before enforcement questions ever arise.
For the market data behind all this — the 23% contraction in London's HMO stock since 2018, the yield arithmetic, the landlord exodus and who is replacing them — see our research article, HMO Conversion Demand Is Accelerating.
What decides approval in an Article 4 borough
Every borough writes its own policy, but London HMO applications are decided on a consistent set of tests:
Concentration / clustering. Most boroughs cap HMO density — Enfield refuses where conversions would exceed 20% of a road or break a 1-in-5 run of houses; Barking & Dagenham uses 10% per road; Haringey applies a qualitative "cumulative impact" test and only supports conversion of houses over 120 m². Check the specific numbers before you buy, not after.
Accommodation quality. Room sizes and amenity standards, set at three levels: the national mandatory HMO minimums (6.51 m² for one adult, 10.22 m² for two, 4.64 m² for a child under 10 — no smaller room may be used for sleeping); the London Plan quality standards (Policy D6); and the borough's own HMO standards, which are often higher — Haringey requires 10 m²+ for a single letting, Enfield sets its own kitchen and communal-space figures.
Amenity and neighbour impact — noise and stacking of rooms, refuse storage that doesn't blight the street, cycle parking, and demonstrating the conversion won't tip on-street parking over the edge.
Fire safety — designed in from the start under London Plan Policy D12, with BS 9991:2024 the operative code (sole version for new design adoption from 30 September 2026).
Licensing then runs in parallel: mandatory licensing for 5+ occupants everywhere, additional licensing schemes in a growing majority of boroughs (typical fees £900–£2,000 per property), and per-room structures in some (Lambeth charges £550/room). Budget for both consents from day one.
What it costs — and what it's worth
The statutory planning fee for a C3→C4 change of use is £610 from 1 April 2026 (the "other changes of use" flat fee — C4 HMOs are not separate dwellings, so the per-dwelling rate does not apply). Submit through the Planning Portal — as almost all applications are — and the Portal's service charge of £75.83 + VAT brings the total payable to £701. An LDC (Proposed) runs at half the equivalent application fee; professional fees for a full London HMO submission — drawings, planning statement, case management — typically sit in the £1,200–£4,000 band depending on scope and complexity.
Against the project economics, those are transaction costs. A well-executed London HMO conversion typically delivers 2–3× the rent of the same building let single, with capital uplift of 20%+ on the converted asset; title-split flat conversions run at 25–35%. On a scheme capturing £100,000–£300,000 of value uplift, the entire planning-and-advisory layer is 1–3% of the value created. The expensive version of this project is not the one with professional fees — it's the one bought in the wrong borough, designed to the wrong room sizes, or enforced against for want of a certificate.
The 2026 changes to have on your radar
Renters' Rights Act Phase 1 — in force since 1 May 2026. Section 21 abolished; all tenancies now periodic; possession via Section 8 grounds (including Ground 4A for student HMOs, allowing summer possession for re-letting). Five tenants now means five individual tenancy relationships — management quality is the moat.
Statutory fees indexed — £610 COU fee from 1 April 2026, rising with CPI annually.
BS 9991:2024 — sole usable version for new design adoption from 30 September 2026.
The Article 4 map keeps tightening — H&F and Harrow are the next likely flips; Merton's confirmation decision lands this summer.
Licensing expansion — the December 2024 General Approval removed the central sign-off threshold, and borough-wide additional schemes keep arriving (Camden renewed December 2025, Islington February 2026, Hackney May 2026).
How to run the decision, in order
Borough and address check — which of the three Article 4 buckets are you in? (Area-based boroughs: check the council map for the exact address.)
Feasibility against the borough's tests — concentration rules, minimum property size, room standards, licensing layer and fees.
Secure the right consent — full COU application in Article 4 areas; LDC (Proposed) where PD applies; LDC (Existing) for established uses in newly-designated boroughs; and the HMO licence in parallel.
Design to the higher standard — wherever borough licensing standards exceed the planning minimums, design to the licensing figure from day one.
Bashkal specialises in residential conversions across London — HMO change of use, flat conversions and lawful development certificates — and we run exactly this sequence for landlords and developers: borough check, feasibility, compliant drawings, submission and licensing coordination. If you're weighing up a conversion anywhere in London, contact us for a technical appraisal before you commit.
Borough Article 4 positions verified against council sources, 5 June 2026. Statutory fees per the Planning Portal fee schedule (1 April 2026); Planning Portal service charge £75.83 + VAT per submission from the same date. Policy and licensing positions change quickly — confirm the current position for a specific property before relying on this guide.
