Up to 15 migrants were found crammed into a three bedroom house in north-west London.
Bunk beds were found packed into small rooms in the house in Kingsbury when council officials carried out a raid this week.
The garden shed at the property also appeared to be lived in.
Brent Council officials received a tip-off that the house was being rented out illegally.
When they carried out a raid on Thursday a Romanian man, who claimed he was the brother of the live-in landlord said six people were living there.
But council inspectors found evidence of as many as 15 people at the address.
Brent Council’s head of private housing services, Spencer Randolph, told the Standard: “We think they heard us coming and they just bolted.
“They’re probably paying about £80 to £100 a week to live there. It’s cheap for the tenants but for the landlords it soon stacks up.”
“This property should be licensed so the landlord is committing an offence.”
A married Romanian couple living in the house on Whitby Gardens said they were paying £600 a month to rent a bottom bunk in a room they shared with other people.
There was also a mattress and clothes found inside the garden shed, indicating that people were also living there.
Another Romanian man living at the address added that young children lived there, which was evidenced by dolls and prams.
Brent Council’s Lead Member for Housing, Councillor Harbi Farah said: “Overcrowded, unsafe properties like this are a danger to the entire community. The landlord had squeezed in as many beds as he could while disregarding basic fire safety principles.”
“The vast majority of landlords and lettings agents in Brent are honest and law abiding, but we take a zero tolerance approach to the minority who think they can treat their tenants like this.”
“Our licensing scheme ensures that landlords maintain their rental properties to an acceptable standard.
Failure to license a rental property could result in an unlimited fine and a criminal record.”
Randolph added that the council was now visiting unlicensed properties twice a week in similar conditions.
As part of the council’s housing scheme, private landlords are required to obtain a licence to ensure properties are rented out at an acceptable standard.
Nearly 100 unlicensed properties have been raided this year, resulting in illegal landlords being fined more than £220,000 and one even received a four month prison sentence.