Almost half of tenants who sublet their property do so without their landlord’s consent, according to new findings from the National Landlords Association (NLA).

The findings come as the government recently announced proposals to introduce minimum room sizes in order to crack down on problems with private rented accommodation such as unauthorised subletting, which often results in overcrowded and cramped properties.

Of the 11% of tenants who say they have sublet all or part of their property before, just 5% did so with their landlord’s permission.

A quarter (26%) of tenants say they have approached their landlord about subletting but have had the request declined, and 63% say they have never asked their landlord about subletting their property.

Overall, the findings show that around a third (32%) of tenants have approached their landlord about subletting their property, with a fifth (22%) of requests being permitted by the landlord.

Carolyn Uphill, chairman of the NLA, said: “These findings indicate that subletting is not common in private rented homes, but worryingly that where it does happen, much of it takes place behind landlords’ backs, without their knowledge or permission.  

“This isn’t something apparently harmless, like putting your flat on AirBnB while you are on holiday. We are talking about individuals looking to deceive their landlord and maximise their personal gains at the expense of proper property management standards and the risk of others. It not only increases the cost of renting for the unwitting sub-tenants, it affects their rights and can reduce security of tenure.

“Subletting can also breach a landlord’s mortgage terms, the conditions attached to licenses granted for letting out shared homes, and invalidate existing insurance products – so they must be aware of the problems it presents.

“The NLA advises all landlords to insert a clause into new tenancy agreements that makes clear sub-letting is only allowed with the landlord’s permission, which should not be unreasonably withheld. This would reduce their exposure to a whole host of unnecessary risks, including hefty fines and even a prison sentence.”