A rogue landlord who illegally carved up family homes to create cramped bedsits and charged tenants hundreds of pounds a month is facing prison unless he pays what is believed to be a record £1.5m penalty for breaking planning laws.

Vispasp Sarkari, 56, from Harrow, north-west London, has been ordered to pay back the money earned over several years from dozens of tenants after he was found guilty of flouting planning rules by converting properties across north London into smaller bedsits without permission and ignoring enforcement notices.

He subdivided suburban homes into what council officials described as “substandard box-room bedsits” in which whole families would live, paying hundreds of pounds per month in rent, often coming from the public purse through housing benefit. Unless he pays the £1.5m penalty Sarkari faces nine years in jail. Judge Lana Wood, making the order at Harrow crown court, described the breaches as “a flagrant abuse” of planning law.

Sarkari has faced repeated enforcement action and last year he was fined for his part in cramming 27 people into a four-bedroom semi-detached house that had been converted into seven tiny flats in Wembley. The property, which Sarkari bought for £220,000 in 2002 according to the Land Registry, was infested with cockroaches and damp. Brent council, whose enforcement officers uncovered the conditions, said six families paying around £650 a month shared insanitary bathrooms and a kitchen that was found to have rat-eaten cupboards and rat droppings.

The latest action taken against him relates to five properties in Brent and Harrow. One in Brent was illegally converted into eight bedsits and four more in Harrow were converted in a similar way, the councils said in a joint statement.

“Justice means taking the illgotten gains off this slumlord millionaire,” said Cllr Keith Ferry, Harrow’s cabinet member for planning, speaking after sentence was handed down. “This is a man who thought he couldn’t be stopped. He was wrong and, thanks to our work with Brent council, Sarkari’s criminal venture is finished.”

But Ferry warned that other landlords continue operating, “ruining our boroughs by running illegal flats and houses of multiple occupation”.

Sarkari was on the London-wide rogue landlord database as a result of last year’s conviction but was not on the national database launched in April because only offences committed from April this year can be included.

A Guardian and ITV investigation in October established that no names had been entered into the database during the first six months it was in operation and that it was not publicly accessible. In a swift U-turn Downing Street said that it would start making the database open to prospective and existing tenants.

The housing minister, Heather Wheeler, said: “We are committed to making sure people who are renting have good quality and well maintained properties, and our rogue landlords database is just one of our policies for doing so, alongside banning orders, civil penalties and rent repayment orders.”

The government has estimated there are more than 10,000 rogue landlords operating nationwide, many of whom own England’s 500,000 houses of multiple occupation.

Last year the government announced new rules insisting that rooms used for sleeping by one adult will have to be no smaller than 6.5 sq metres, and those slept in by two adults will have to be no smaller than 10.2 sq metres. Rooms slept in by children of 10 years and younger will have to be no smaller than 4.6 sq metres.

Previous convictions appear not to have deterred Sarkari. In 2008 he was fined £2,800 for a string of fire safety offences and the following year he was fined £5,000 for failing to comply with a planning enforcement notice relating to another property in Wembley. In 2012 a confiscation order of more than £300,000 was made against him under the Proceeds of Crime Act for flouting planning laws and he paid it in full. Then three years later he was fined £10,000 and ordered to perform 150 hours of community service over gas safety breaches at a property in Wembley. Finally, in December last year he was fined £13,400 for breaches of a selective licence including fire safety and cockroach infestation.

To date, Sarkari has faced fines, confiscation orders and legal costs of £1,844,342.

Sarkari’s legal representatives have been contacted for comment.