A rogue landlord stuffed a filthy and dangerous three-bedroom house – with 26 mattresses.
Officers found more than 20 men living in “appalling and unsafe” living conditions and could barely enter the house because mattresses were “jammed up against the doors”.
The council said it was “one of the worst” illegal HMOs it has ever uncovered.
Police are now hunting the rogue landlord, who was taking home £1,000 a week from his despicable racket.
Every room in the illegal HMO, except for the kitchen and bathroom, contained bed spaces – including the “tiny, windowless” loft space.
Police and Brent’s enforcement team raided the three-bedroom semi-detached house in Kingsbury, north west London, in the early hours of Thursday morning.
The raid was prompted by complaints from residents about the number of men seen coming and going from the house in the suburban street of Princes Avenue.
The disgusting conditions, for which the men were paying between £30 and £50 to live in, also had faulty smoke alarms, poor ventilation and fire hazards.
A spokeswoman for Brent Council said it was “one of the worst” illegal HMOs it has uncovered.
She said: “Aside from seeing rodents or cockroaches it is one of the worst we have seen.
“The loft was just appalling – really awful conditions.”
Councillor Eleanor Southwood, cabinet member for housing and welfare reform, said: “We have a zero tolerance policy against landlords who exploit tenants by housing them in slum-like conditions.
“No tenant in Brent should believe that they are powerless against a landlord who takes their money in exchange for squalor.
“We are here to help tenants fight back against rogue landlords by taking them to court.”
From October 1, any property that is rented out to five or more people who are not all related will require a mandatory licence.