Eleven people were found living crammed in a three-bedroom house with mould-blackened ceilings.
The tenants were found to be sleeping in every room inside the house except for the kitchen and bathroom, Brent Council has said.
The housing enforcement team and police raided the semi-detached home in West Hill, Wembley, after a tip-off from a neighbour.
According to the council, the house did not have a house in multiple occupation (HMO) licence.
During the search, it was found that a polystyrene ceiling gave way inside the kitchen and damp and black mould covered the walls and ceiling.
Officers also discovered there were no fire safety doors or a fire alarm system.
Tenants told Brent’s licensing enforcement team that they were paying a combined rent of more than £2,000 to their landlord to live in the property’s squalid conditions.
Cllr Promise Knight, cabinet member for housing, homelessness and renters’ security, said: “It is shocking and horrifying that rogue landlords make a profit from keeping people in dangerous and slum-like conditions like this.
“People in vulnerable circumstances tend not to know what rights they have as renters.
“Rogue landlords who exploit their tenants’ vulnerability will find themselves facing hefty fines and possibly a criminal conviction. We will use whatever powers we have to hold them to account.”
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