Thirteen people were found “absolutely packed” into a three-bedroom house in Newcastle, the BBC has found.
The bath had been ripped out and a bunk bed put in its place, officials found when they visited the property in Ponteland Road, Blakelaw, in January.
None of the people, who were restaurant workers, knew each other, Paula Davis from Newcastle City Council said.
The council is now pursuing the private landlord for operating a house in multiple occupation without a licence.
The Home Office said of the 13, three women and seven men aged between 20 and 51 were arrested for either overstaying their visas or on suspicion of obtaining leave to enter the UK by deception.
Four have subsequently been removed from the UK and one remains detained pending their removal from the UK.
Three have made further immigration applications and must report regularly to the Home Office while their cases are dealt with. Two faced no further action.
More than one in 10 privately-rented homes across the North East are unfit to live in, according to the Ministry for Housing, Communities and Local Government. Newcastle Council said it dealt with some 1,200 complaints each year.
The BBC’s Inside Out went out with the council’s environmental health officers and saw properties with no heating, hot water or smoke alarms.
Others had broken sockets which carried a risk of electrocution, windows and doors that did not open and mould on the walls.
Ms Davis, the council’s public protection and neighbourhoods team manager, told Inside Out: “There are an awful lot of vulnerable tenants, old people, young people, people who have migrated to the city and maybe don’t speak English as a first language.
“They wouldn’t know who to complain to. That’s the group of people we are most concerned about and we most want to help.”
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Landlords who ignore their responsibilities could face a fine from the council of up to £30,000 per offence.
Newcastle council only took on these powers recently and it is yet to use them.
But plans are under way to extend its licensing programme to cover more than 18,000 properties.
Landlords would need pay up to £750 a home for a permit guaranteeing it was up to scratch.
Newcastle City Council deputy leader Joyce McCarty said: “The money we get can’t be used for anything other than the scheme.
“That income will provide us with a team of officers who can support landlords and make sure the tenants are living in decent homes.”
But she admitted the scheme would “probably” push rents up for tenants.
The National Landlords Association said: “We do not support the scheme as Newcastle council lacked the evidence to support its introduction… they would be better off taking a more targeted approach.”
You can see more on this story on Inside Out in the North East and Cumbria on Monday 25 February at 19:30 on BBC One or afterwards on the iPlayer.
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