You drive past on a Sunday and there are three cars on the drive. The rent arrives from a bank account with a name you don’t recognise. A neighbour mentions the “new couple” downstairs. Your tenant, when asked, is vague.
Unauthorised subletting is one of the few tenancy problems where the law is firmly on the landlord’s side — considerably more firmly than most landlords realise. There is a statutory implied term in every tenancy prohibiting it without your consent, you don’t have to be reasonable in refusing, and a tenant who sublets the whole property can permanently lose their security of tenure.
What you must not do is act on suspicion, or take matters into your own hands. This guide covers how to establish what’s actually happening, the legal position since the Renters’ Rights Act, your realistic options, and the licensing trap that can turn your tenant’s breach into your £30,000 problem.
Key takeaways
- Section 15 of the Housing Act 1988 implies a term into every periodic assured tenancy that the tenant must not sublet or part with possession of the whole or any part without your consent. Since all tenancies became periodic on 1 May 2026, this now applies universally.
- You do not have to act reasonably when refusing consent. Section 19 of the Landlord and Tenant Act 1927 is expressly disapplied.
- If a tenant sublets or parts with possession of the whole property in breach, the tenancy ceases to be assured and can never become assured again.
- Unauthorised subletting can make your property an unlicensed HMO — exposing you to a civil penalty of up to £30,000 and a rent repayment order of up to two years’ rent.
- Ground 12 (breach of tenancy) needs two weeks’ notice and is discretionary. Ground 14 covers nuisance or illegal use and can be served immediately.
- Never change the locks or remove anyone yourself. You need a court order, and unlawful eviction is a criminal offence.
What subletting actually is
Subletting is where your tenant grants someone else a tenancy of all or part of the property. The subtenant pays your tenant; your tenant remains liable to you. It is genuinely different from three other things landlords often confuse it with — and the distinction changes your response.
| Arrangement | What it means | Your position |
|---|---|---|
| Subletting | Tenant grants a tenancy of all or part to someone else | Breach without your consent |
| Lodger | Tenant takes in someone who shares living space with them, with no exclusive possession | Still requires consent under Section 15 (parting with part) |
| Permitted occupier | Someone named in the agreement who may live there but has no tenancy | Legitimate if you agreed to it |
| Assignment | Tenant transfers the whole tenancy to someone else | Requires your consent; the original tenant drops out |
A partner moving in is usually a permitted occupier question, not subletting, and is normally handled by adding them to the agreement. Our guide to permitted occupiers covers where that line falls. Short-term holiday letting through a platform is a different beast again — see dealing with a tenant subletting on Airbnb.
The legal position, and why it’s stronger than you think
You don’t need a clause in the agreement
Landlords often panic on discovering their tenancy agreement has no subletting clause, or can’t find their copy. It rarely matters.
Section 15 of the Housing Act 1988 implies a term into every periodic assured tenancy that, except with the landlord’s consent, the tenant shall not assign, sublet or part with possession of the whole or any part of the property. Before May 2026 this only caught periodic tenancies, so fixed-term ASTs relied on an express clause. Now that the Renters’ Rights Act has made every assured tenancy periodic, the implied term applies across the board.
Better still, section 15 expressly disapplies section 19 of the Landlord and Tenant Act 1927 — the provision that normally requires consent not to be unreasonably withheld. You may refuse consent without giving a reason. That is an unusually strong position in modern landlord and tenant law.
Subletting the whole property destroys the tenancy’s protection
This is the provision most landlords have never heard of, and it is powerful.
An assured tenancy only exists while the tenant occupies the property as their only or principal home. Under section 15A of the Housing Act 1988, where a tenant parts with possession of the whole property, or sublets the whole (including subletting part and then the remainder) in breach of an express or implied term, the tenancy ceases to be an assured tenancy and cannot subsequently become one. The loss is permanent, even if the tenant later moves back in.
In plain terms: a tenant who moves out and rents the whole place to someone else has thrown away their security of tenure. You are no longer confined to the Section 8 grounds.
Two important caveats. First, this applies to the whole property — a tenant who takes in a lodger while continuing to live there is in breach, but keeps assured status. Second, losing assured status does not mean you can remove anyone yourself. You must still end the contractual tenancy properly and obtain a possession order through the court. Evicting without one is a criminal offence under the Protection from Eviction Act 1977. Take legal advice before relying on this route.
Handling suspected subletting, step by step
Payment records, correspondence, a properly noticed inspection. No surveillance, no turning up unannounced.
In writing. Give them a genuine chance to explain — it may be a lodger, a guest, or a misunderstanding.
If the occupancy has tipped the property into HMO territory, this is now urgent for you, not just the tenant.
Cite the term breached, set out the evidence, give a clear deadline and state the consequence.
Sometimes the commercially sensible answer is to reference the occupier and bring them onto the agreement.
Ground 12 for breach, or Ground 14 where there is nuisance or illegal use. Always via the court.
Why it matters
Unauthorised subletting isn’t just a matter of principle. The practical exposure is real:
- Unvetted occupiers. Nobody has referenced them, checked affordability, or verified their right to rent.
- Insurance. Most landlord policies require you to know who is in occupation. An undisclosed sublet can invalidate cover exactly when you need it.
- Mortgage terms. Buy-to-let lenders almost always prohibit subletting without consent.
- Overcrowding and wear. Six people in a three-bed causes damage that six weeks’ deposit won’t cover.
- Criminal use. At the serious end, unexplained occupancy is a marker for cannabis cultivation and other criminal use.
- Rent-to-rent gone wrong. Some “tenants” are running an unlicensed business from your asset — see the risks of renting to serviced accommodation operators.
The HMO trap that lands on you
This deserves its own section, because it is the risk landlords most consistently miss.
If your tenant’s subletting means the property is now occupied by three or more people forming two or more households and sharing facilities, it may have become a house in multiple occupation. Mandatory licensing applies to HMOs occupied by five or more people from two or more households, and many councils operate additional licensing schemes covering smaller HMOs.
The offence of managing or controlling an unlicensed HMO falls on the person having control of, or managing, the property. Councils have taken the view that this can include the owner, even where the occupancy arose without their knowledge. The consequences are serious:
- A civil penalty of up to £30,000, or an unlimited fine on conviction.
- A rent repayment order. For offences committed on or after 1 May 2026 the Renters’ Rights Act doubled the maximum to two years’ rent.
- Potential entry on the database of rogue landlords, and difficulty obtaining possession while unlicensed.
“My tenant did it without telling me” is not a complete answer. It may support a reasonable-excuse defence, but only if you can show you took reasonable steps — regular inspections, prompt action on discovery, contemporaneous records. Which is the strongest practical argument for inspecting properly. Our HMO licensing guide sets out the thresholds.
Gathering evidence — lawfully
Suspicion is not evidence, and how you obtain evidence matters. Older advice to “knock on the door and see who answers” or quiz the neighbours is worth treating with care: you have data protection obligations, and heavy-handed investigation can itself amount to harassment.
Legitimate warning signs and sources:
- Rent arriving from an unfamiliar account or split across multiple payments.
- The property advertised on a letting or short-stay platform.
- Post or deliveries in unknown names, or extra names on the electoral roll.
- Utility consumption far above the expected level for the household.
- Your tenant becoming difficult to reach, or consistently avoiding inspections.
- What you observe on a properly arranged inspection.
Arrange inspections properly: at least 24 hours’ written notice, at a reasonable time, and with the tenant’s agreement to enter. You have no right to force entry, and doing so risks a harassment claim that will overshadow the subletting entirely. Our guide to rental property inspections covers the process. Record what you find in writing, dated, with photographs of communal areas only.
The formal warning letter
Once you’re satisfied there is a genuine breach, put it in writing and send it by a method you can prove. Keep the tone factual — this document may end up in front of a judge.
Dear [Tenant],
Re: Unauthorised subletting at [property address]
I am writing about the occupation of the above property.
Under section 15 of the Housing Act 1988, it is an implied term of your tenancy that you may not sublet or part with possession of the whole or any part of the property without my consent. [Clause X of your tenancy agreement also provides for this.] I have not given consent.
I have reason to believe the property is currently occupied by one or more persons who are not party to the tenancy. My evidence is: [set out factually — dates, observations, payment records].
Please respond in writing within 14 days of the date of this letter, either confirming that any unauthorised occupiers have left, or providing full details of the occupiers so that I can consider whether to grant consent and carry out the necessary referencing and right to rent checks.
If the breach is not resolved, I will consider serving notice seeking possession under Ground 12 of Schedule 2 to the Housing Act 1988. I would also draw your attention to section 15A of that Act, under which a tenancy ceases to be an assured tenancy where the tenant sublets or parts with possession of the whole of the property in breach of the tenancy.
I would much rather resolve this by agreement, and I am happy to discuss it.
Yours sincerely,
[Name]
Send it by recorded delivery and by email, and keep proof of both.
Your possession options
Section 21 was abolished on 1 May 2026, so there is no longer a no-fault route. Everything now runs through Section 8 on the prescribed form.
| Ground | Use | Type | Notice |
|---|---|---|---|
| Ground 12 | Breach of a term of the tenancy — the standard route for subletting | Discretionary | 2 weeks |
| Ground 14 | Nuisance, annoyance or illegal use by occupiers or visitors | Discretionary | None — but no order for 14 days |
| Ground 13 | Deterioration of the property caused by the occupiers | Discretionary | 2 weeks |
All three are discretionary: the judge decides whether possession is reasonable. That makes your evidence and your conduct central. A landlord who investigated properly, warned clearly, offered to regularise the arrangement and kept a calm paper trail is in a far stronger position than one who arrives with hearsay and an angry email.
Remember too that a deposit that isn’t properly protected, with prescribed information served, will block a possession order under these grounds. Check that before you serve anything. If the tenant stays put after notice expires, see our guide on what to do when a tenant won’t leave.
What about the subtenant?
An unlawful subtenant generally has no better right to remain than the tenant who granted it, so their occupation ends with the head tenancy. You are not responsible for rehousing them, and any claim they have is against your tenant.
In practice, name any occupiers you know about in the proceedings and make sure the order covers all occupiers, so that enforcement isn’t frustrated later. And treat them decently — they are often people who paid a deposit in good faith and have been misled.
Should you just regularise it?
Possession is slow, expensive and uncertain. Before committing to it, ask whether the commercially better outcome is to bring the arrangement into the open.
If the occupier is a reasonable person in stable work, you can reference them, carry out a right to rent check, and either add them to the agreement or grant consent to the sublet on terms. You end up with a vetted occupier, a compliant property and no void — and you can make consent conditional on the licensing position being sorted out.
Regularise where the people are acceptable and the numbers work. Pursue possession where the occupancy is unsafe, the property has become an unlicensed HMO you can’t licence, there’s criminal activity, or the tenant has simply stopped being straight with you.
Common mistakes
- Changing the locks. Unlawful eviction is a criminal offence and attracts damages. Never.
- Accepting rent knowing about the breach without reserving your position. It can be argued you waived it. Say in writing that rent is accepted without prejudice.
- Assuming no clause means no protection. Section 15 implies the term for you.
- Ignoring the licensing position. Your tenant’s breach can become your offence.
- Investigating heavy-handedly. Repeated unannounced visits can amount to harassment.
- Giving verbal consent. Always in writing, always specific to named people.
Preventing it
Include an express subletting clause even though section 15 implies one — it makes the position obvious to the tenant. Explain at sign-up that anyone moving in must be approved, and that you’ll usually say yes to a reasonable request. Most unauthorised subletting happens because tenants assume they’ll be refused.
Then inspect regularly and keep records. Six-monthly inspections, properly noticed and written up, are the single most effective control — they catch problems early and they are exactly the evidence you’ll need if a licensing officer ever asks what steps you took.
Frequently asked questions
My tenancy agreement doesn’t mention subletting. Am I stuck?
No. Section 15 of the Housing Act 1988 implies a term into every periodic assured tenancy prohibiting subletting or parting with possession without the landlord’s consent. Since all assured tenancies became periodic on 1 May 2026, this applies whether or not your agreement says anything.
Do I have to be reasonable in refusing consent?
No. Section 15 expressly disapplies section 19 of the Landlord and Tenant Act 1927, so the usual requirement that consent must not be unreasonably withheld does not apply. You may refuse without giving reasons.
What if I gave verbal permission?
Verbal consent can still be consent, and a tenant may rely on it, so don’t assume you can simply reverse it. Confirm any agreed position in writing now, including exactly who may occupy and on what terms.
Can I increase the rent because my tenant is subletting?
Not as a penalty. Rent increases must follow the statutory procedure — one increase in any 12-month period, with the required notice, and the tenant may challenge it at the First-tier Tribunal. You can, however, negotiate revised terms as a condition of granting consent.
What happens to the subtenant if I get possession?
An unlawful subtenant has no better right to remain than the tenant who granted it, so their occupation ends with the head tenancy. You are not responsible for rehousing them. Name known occupiers in the proceedings so the order covers them.
Could I be fined because of my tenant’s subletting?
Yes. If the occupancy makes the property a licensable HMO, the offence of managing or controlling an unlicensed HMO can fall on you. Penalties include a civil penalty of up to £30,000 and a rent repayment order of up to two years’ rent for offences on or after 1 May 2026. Regular inspections and prompt action support a reasonable-excuse defence.
Can I evict the occupiers myself?
No. You need a court order and, where necessary, county court or High Court bailiffs. Changing locks or removing belongings is unlawful eviction, a criminal offence under the Protection from Eviction Act 1977, and exposes you to substantial damages.
Written by the Landlords Portal team — experienced UK landlords covering the private rented sector in England. This article is general information, not legal advice. Subletting cases turn on their facts and the section 15A route in particular is technical — take advice before serving notice or relying on loss of assured status.
