Almost 100 beds in sheds have been shut down over the past two years in a crackdown on dodgy landlords.
Redbridge Council has taken action to close 93 outbuildings which have been illegally rented out as accommodation.
The authority said many of the outbuildings did not comply with housing safety standards or planning policy, and can be dangerous and poor quality places to live.
Officers said they can also be a nuisance to people living in neighbouring properties.
Cllr Helen Coomb, cabinet member for economy, regeneration and planning, said: “Beds in sheds are completely unacceptable and we are determined to rid them from our borough.
“They are often unsafe and rented to vulnerable people by greedy landlords who are more interested in profit rather than their basic responsibilities.
“Our blitz on beds in sheds sends out a loud and clear message to all those who build or let out unauthorised outbuildings – they will not be tolerated and we will take action.”
As part of a joint operation led by planning enforcement and housing standards officers, the council has investigated 454 suspected illegal outbuildings since 2013.
Those investigations have led to five landlords being prosecuted for offences relating to occupied outbuildings, with court fines and costs totalling £62,065.
Officers have served 63 Housing Prohibition Orders to close down outbuildings which did not meet housing standards, and served 30 Planning Enforcement Notices on buildings which did not comply with policy and standards for residential properties.
It has also prevented and adapted a further 73 potential or suspected unlawful outbuildings through voluntarily changes or closure. No action was taken following the other investigations.
To report suspected unlawful use of an outbuilding, visit redbridge.gov.uk/planning
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