These unauthorised arrangements are most often uncovered when neighbours report unusual activity or a stream of unfamiliar visitors (31%). Routine inspections by landlords account for 28% of discoveries, while 24% stem from complaints about noise or property damage from nearby residents.
Increasingly, landlords are turning to online sleuthing to spot illicit sublets. Around 15% found clues on social media or other digital platforms, and 20% discovered their property advertised on rental sites.
Almost half of landlords (43%) carry out routine inspections every six months, while 74% check their properties at least once a year. Among those who’ve uncovered unauthorised subletting, nearly two-thirds (64%) said the issue arose within the past year.
When faced with a secret sublet 34% of landlords responded by issuing a formal warning to the tenant, and 30% reported the matter to their letting agent or property manager.
Some chose a more flexible route—26% permitted the sublet to continue under revised terms or with written consent, while 27% sought legal advice but opted not to take further action.
Others took firmer steps: 27% demanded the subtenant vacate immediately, and 25% initiated eviction proceedings against the original tenant. Additionally, 22% responded by raising the rent or applying a subletting surcharge.
In response to the rising concerns over unauthorised subletting, 77% of landlords have amended their tenancy agreements to tighten controls. More than a third (35%) have introduced explicit penalties for tenants who sublet without consent, while 34% now require formal approval for guests or subletters staying beyond a specified duration.
Additionally, 28% have clarified existing subletting terms to avoid ambiguity, and 38% have inserted a dedicated clause banning subletting without written permission. However, 10% of landlords see no need to revise their agreements at all.
A spokesperson for the business insurance firm which commissioned the research, comments: “Landlords work hard to look after their properties, so it’s understandable that secret subletting is a real worry. The company urges landlords to ensure that they stay up to date with their periodic property checks and make tenants aware about rules in relation to subletting or moving in additional tenants.”
Subletting isn’t universally rejected by landlords—more than half (53%) say they’re open to the idea, provided certain safeguards are in place. These include setting clear terms and ensuring adequate insurance (16%), conducting thorough checks on subtenants (13%), requiring subtenants to meet the same criteria as original tenants, such as references and credit checks (13%), and restricting subletting to short-term periods like summer holidays or student breaks (11%).
Still, resistance remains. One in five landlords (18%) argue that subletting compromises their ability to manage the property effectively, while 8% point to negative experiences—either firsthand or shared by peers—as reasons for their firm opposition.
The spokesperson for the insurance firm, added: “Our research shows that not all landlords are opposed to subletting, but the security of knowing who’s living in their property and that the right checks are in place are important. In this case, being upfront with tenants about what is allowed, and putting clear agreements in writing, can help prevent misunderstandings and protect everyone involved.
“As always, having open communication with the tenants is a great way to create a safer, more trusting renting environment for both landlords and tenants."