Farook Owadally was ordered to pay a £90,000 fine, £400,000 confiscation order and £40,000 in costs by Southwark Crown Court.
He had divided what was a three-bedroom home into eight separate flats without bothering to get planning permission.
He was found to have been charging more than £1,000 a month in rent for each of them, which according to Westminster City Council were generally “simply a small room”.
Most did not meet the minimum size requirement of 37sqm for new one-bedroom flats, with one just 18sqm.
The council had issued enforcement notices dating back to January 2012 calling on Owadally to remove the flats built into the property, demolish a third floor extension, and return it to its former condition as a shop with a maisonette above.
However, Owadally made no attempts to engage with planning officers, which the council argued was so that he “could continue to profit over an extended period of time”.
He now has three months in order to pay the confiscation order, and six months to pay the costs and fines to the court.
Councillor Richard Beddoe, the Westminster City Council cabinet member for place shaping and planning, said this was “a straightforward case of the law catching up with an unscrupulous person”.
He continued: “Our planning teams aren’t just ticking boxes and filling in forms for fun – we have planning rules for a reason, to make sure housing is fit for purpose and safe.”