A cramped three-bedroomed house was home to 14 tenants paying up to £400 a month each in rent.
Landlord Sohaib Anwar converted the family home into a nine bedroomed property with shared a shared kitchen and bathroom.
Ealing Council housing officers ordered him to change the house back to a family home, but Anwar ignored their requests.
At Ealing Magistrates Court, Anwar pleaded guilty to breaking planning rules and was fined almost £42,000 for the offence.
Council leader Councillor Julian Bell said: “Anwar was given several chances to comply with planning laws but chose to line his own pockets.”
Illegal tree lopping
Another landlord who lopped branches off three protected oak tress was fined £3,000 and ordered to pay £1,200 costs.
Shabbir Ahmad, of Tilgate, Crawley, admitted to the town’s magistrates that he broke a tree preservation order.
The trees were growing in the garden of a letting property he owns.
The court heard that the trees were damaged by the lopping and will probably die.
Councillor Colin Lloyd, cabinet member for environment, said: “These oaks are protected because they are important to the residents in the area, they are part of the historic fabric of the town, and impressive or attractive specimens add to the appeal of Crawley’s landscape.
“Once a tree is altered, or in the worst case cut down, it is lost forever. Which is why we take action and why the magistrates have imposed such a heavy fine.”
Landlord Wimalendran Jeyaruban and letting agent Chaudry Amir Ijaz were found to be letting a house in multiple occupation (HMO) without a licence after a fire started in the property.
Each must pay fines of £3,000 and costs of £2,500 after they were found guilty of the offence at Croydon Magistrates Court.
Seven people were led to safety by fire crews after a blaze at the flat in January. Five neighbours were also evacuated.
Five tenants were living in the flat and paying rent of £150 each.
Croydon Council had already ordered Jeyabruben to stop letting the flat as an unlicensed HMO, but let the property to Ijaz who continued to rent the flat without a licence to tenants.