Attempts by Airbnb to crackdown on rogue landlords using its site have little chance of succeeding, London councils have told the BBC.
The move to limit Airbnb hosts from renting properties for more than 90 days was announced in December.
London boroughs have warned that short-term lets are pushing up longer term rental prices in the capital.
But nearly a third of all boroughs told the BBC the time limit would not slow the growth of short-term letting.
Airbnb, an accommodation listing website, said the impact of short-term lets and home-sharing websites on rental prices in London was "negligible".
Last year, it commissioned the Institute for Public Policy Research (IPPR) to investigate the impact of short-term lets on London's rental market .
Airbnb said the IPPR report found "entire homes" booked on the site at least once a year made up less than 1% of total private housing stock in London in 2015.
But the study also showed 11% (2,444 properties) of Airbnb's entire home rentals were let for more than six months of the year.
'Nowhere to live'
The IPPR found landlords were, in some cases, removing properties from the long-term rental market altogether and offering their properties for rent on a series of short-term lets instead.
In turn, this piled pressure on long-term rental prices due to a lack of available properties, the report said.
It also found some Airbnb hosts may have been offering properties for rent illegally.
Events organiser Daniel Thomas has been looking for an affordable room to rent in the area for over a year.
Mr Thomas, who commutes from Slough to Ladbroke Grove, said: "Lots of young people here are looking for properties for the first time, and they're all just going to tourists, so we have nowhere to live."
The law states owners cannot let property for more than 90 days in a given year on a short-term let.
If an owner wants to let for longer, they must seek planning permission for a "change of use" from their local council.
Seven London boroughs - Camden, Hammersmith, Haringey, Islington, Lewisham, Waltham Forest, Westminster - have now called for tougher legislation to prevent illegal lettings.
A Camden Council spokesman said: "There is a clear justification for doing so given the detrimental impact short-term letting is having on housing availability in London."
Diarmard Ward, executive member for housing at Islington Council said: "Airbnb and other short-term letting sites push up rents and they also reduce the number of homes for people who want to rent long term."
Airbnb's northern Europe boss, James McClure, told BBC London the company was introducing the 90-day limit "to forestall any potential danger down the road".
"That's why we're looking to implement automatic limiting to ensure the law is respected and it's up to councils to decide the best use and mix of properties in their area," he added.
The Department for Communities and Local Government said any landlord breaching the 90-day limit "faces a hefty fine", and added it is up to local councils to enforce the law.
A government spokesman praised Airbnb's policy and encouraged other services to follow suit.
'Carry on as before'
But commercial landlords operating on Airbnb told BBC London the 90-day limit would have no effect.
One, who has three homes listed on the site but did not want to be named, said: "I'll just carry on as before. When the 90 day rule comes up, I'll re-register the homes I have so it looks like they're different homes... a few metres away.
"I know many other landlords planning to do the same thing."
Another, Bulent Boytorun, who rents four homes on Airbnb, said he may move his business to alternative home-sharing platforms.
All 33 of London's boroughs, including the City of London, were asked whether they believed all home-sharing websites should block illegal lets.
Twelve of the 28 the councils that responded to BBC London said they supported it.
But when BBC London asked other competitors in the short-term letting market sites if they enforced the 90-day rule or planned to do so, none said they did.
A spokesperson for TripAdvisorRentals, which lists about 8,000 London properties, said: "To list on our site, homeowners and managers must agree to our terms and conditions, which require a property to be operated in accordance with all local laws and regulations."