Housing enforcement teams in Harrow found a house crammed with 28 people, men hiding in a shed sandwiched between mattresses and a person found sleeping in a storage area - all in a night's work.
Council officers found a total of 17 properties operating illegally, with no HMO (house of multiple occupancy) licence when they carried out raids on 32 properties on Wednesday (November 8).
They were sharing a tiny bathroom and kitchen with no fire safety or smoke alarm.
Officers are currently looking to find the landlord so that they can fix the property, deal with the overcrowding and have it licensed.
Men were found hiding in a shed sandwiched between mattresses, the council said, in a different property in the Edgware area.
The two-storey house had around 15 people living there, including three children – the youngest being an eight-month old baby.
A Harrow council spokesman said: "Some of the other things uncovered were illegally converted outhouses, a licensed property that was overcrowded and a person found sleeping in a storage area who refused officers entry. They claimed there were on holiday.
"Officers will now follow up with further visits and checks with landlords and agents to get these properties licensed with a view to prosecute."
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