Property management companies are encouraging landlords to break strict short-term letting laws in London, an undercover BBC investigation has found.
Landlords cannot legally rent out their homes in the capital for more than 90 nights a year under regulations.
However, some firms were secretly recorded explaining methods to get around this, such as using new photos to make listings appear as new.
Westminster North MP Karen Buck said it "undermined" London's housing market.
Short-term letting companies, such as Airbnb, have transformed the tourism industry by making it easier for anyone to rent out their home to visitors.
But, landlords in London are only allowed to let their homes out for more than 90 nights a year on short-term lets if they receive planning permission from the council.
Airbnb said it used software that stopped anyone from renting out short-term lets for longer than 90 days with an inbuilt "counter".
The counter begins from the moment a property is listed.
A senior manager from Hostmaker - one of the larger management companies for short-term rentals - was secretly recorded explaining how the firm could help landlords get around the law.
"We do a new listing for you. We delist this one, start from scratch again", she said.
"We will do fresh photos. If you use existing photographs, Airbnb's algorithm tracks it as the same property. We do everything new. And then your 90-day ticker will start from scratch again."
Hostmaker said it was committed to complying with regulations and would "immediately conduct a full internal investigation".
An agent from another management company, Guestready, was also separately secretly recorded.
She said: "We'll create another listing for you and they won't even know.
"It's not that you shouldn't really do it, it's just that everyone does it."
There was no response from Guestready when approached for a comment.
Westminster North MP Karen Buck, who has campaigned for greater regulation on short-term lets, described the undercover footage as "absolutely shocking".
"It undermines everything we were told about how short-let accommodation would work and it's really deeply dispiriting", she said.
Airbnb told the BBC it had a team that worked to prevent, detect and tackle attempts to avoid automated night limits and would not tolerate efforts to circumvent these systems.
Other management companies said they would advertise lettings on other short-term letting websites in attempts to help landlords bypass the law.
Maxime Leufroy Murat, CEO of Cityrelay, was filmed offering this advice.
He said: "If you want to stop at 90 days, we can stop at 90 days. If you want to go above, we can help you go above.
"We will never do more than 90 days on Airbnb - but you will get bookings from bookings.com, HomeAway, TripAdvisor.
"It might be 180 days in the end. 200 days."
In response, Cityrelay said: "If our clients want to rent their property on short lets for over 90 days per calendar year, we explain to them they would need to seek planning permission."
Housing lawyer David Smith said: "They are misinforming and misleading the people they are dealing with by suggesting to them that what they are doing is not unlawful.
"It is and it should stop."
You can watch the full undercover investigation on BBC London TV news at 18:30 and 22:25 and Inside Out London on BBC One on Monday 25 February at 19:30 GMT.