More than 100 criminal prosecutions have been secured against landlords since the start of an enforcement crackdown by Brent council in London.
The 101st was reached in Willesden Magistrates Court when an illegal sub-letter without a licence was hit with thousands of pounds worth of fines.
Arthur Zurvskij was found guilty of illegally sub-letting a five bedroom house in Willesden to seven tenants.
Instead of securing a House in Multiple Occupation licence from Brent council, Zurvskij - director of Skyline Property Management; a name he later changed to Enox UK Ltd - rented out the property through Ludlow Thompson letting agency.
The owner of the property, who lived in the United States and had legally handed over control of his property to Ludlow Thompson, believed that the property was being rented out to a single family.
During the trial, Willesden Magistrates Court also heard that Zurvskij had not sought written permission from the landlord to let the house to more than one household. He was ordered to pay £2,250 in fines while his company Enox UK Ltd, had a £8,000 fine.
A Brent enforcement officer says: "Breaching the law on HMO is very serious. If found guilty, the landlord or person in charge of the property is left with a criminal record. The potential fines are now unlimited.”
The council's zero tolerance policy includes prosecutions against tenants who illegally sublet the property they are renting.